First off I would check the Event viewer - Start/Control panel/Administrative tools/Event viewer on all 3 machines and read and compare the red or yellow markers to see if there is anything there. Having had this issue myself I found my wife's computer seemed to take over things and my machine would not /could not connect to the net.

I went through 3 routers including a Linksys and Dlink without success. This had been an ongoing issue with a few of us members on a computer forum I belong to.

The cure was as simple as removing Zonealarm and using the free Comodo or any other firewall instead. Are you using Zonealarm?

Failing that I would swap the CAT5 cable running from the modem to the router to see if it was defective. Just swap it with one going from the router to a computer to see if it is the problem.

When the connection goes out, it goes out on all 3 computers at once, though -- do you really think something like ZoneAlarm could be affecting all 3 at once? We do run that on our two hardwired computers, but not on my laptop. There are no firewall or anti-virus software similarities between my laptop and the two other computers...

We'll try swapping the cable and see if that does anything. We have a ton of them laying around :)

I dunno ... fwiw
Might be something as simple as a neighbors laptop trying over and over wirelessly to connect to your router, accidentally most likely. Could be a far off neighbor with a good big antenna. Eventually causing the router to reboot, which takes about a minute on most of them to re-establish connectivity.

Same with a neighbor and 2.4ghz phones. Same with your 2.4ghz phones... happened to me - almost clockwork afternoon modem resets after buying a new 2.4 phone, phone worked fine as long as I wasnt sitting at laptop... then a few weeks later all of a sudden for no reason I can think of the afternoon reboots started ..... so I moved to the newer 1.9 Ghz digital signal phones to end it.
Still on occasion, will loose networking for a minute - think maybe a neighbors phone. My router will be blinking a reboot. Could be occasional someone doing a ping attack or something, log clears on reboot, no way to tell.

Fire truck or ambulance passes my home directly, router goes into reboot too. We know they got radio's. Apparently strong ones.

Try turning off the logging in the router. I've had log files cause two different brand routers to go into a resets when full or something. Disabling logging fixed both.

rivkader-
How do you get your signal in the first place: DSL, cable, what? I'm thinking this may not be an equipment problem. It could be a problem with your provider, or it could be the quality of the cabling that comes into the house. For example, if you have DSL, it could be an iffy copper pair running to the service drop or running inside your house. If it's cable, it could be slightly damaged insulation that gives an intermittent fault.

I agree with Owbist ... and disabling Zonealarm was not enough to solve the problem in my case. ZoneAlarm had to be completly uninstalled in order for my router to work properly.

Jodi-

Well if Mikie or kudju9's ideas do not solve your issues why not remove Zonealarm from just one computer to see if it is or is not helping/hindering. As Jodi noted, disabling Zonealarm did not do the trick, removal cured it for me. I learned long ago to never doubt even the whackiest suggestions as long as you know no harm can come to your computer.

It could be a problem with your provider, or it could be the quality of the cabling that comes into the house.

I really don't think it's our cable. As I said in my original post, we directly connected one of the computers to our cable modem for a few days. During those 3 days, we didn't have a single dropped connection. We also had great connections BEFORE we switched to the wireless router (we used to use a switch) as of 2 months ago.

First off I would check the Event viewer - Start/Control panel/Administrative tools/Event viewer on all 3 machines and read and compare the red or yellow markers to see if there is anything there.

Took a look -- nothing there coincided with any of our dropped connections in the past couple of days.

As Jodi noted, disabling Zonealarm did not do the trick, removal cured it for me.

I'm sorry, I just don't buy that ZoneAlarm could be causing this. I've looked at all the computers. It's actually only installed on one machine (my husband's). His computer isn't even running right now, and yet I've dropped my connection 3 times in the past 6 hours. How could ZoneAlarm on a machine that is not even turned on have anything to do with it?

I'm concerned that it may be Mikie's suggestion -- interference from outside. If so, I'm not sure what we can do to resolve it.

You can try making a reflector for your routers antenna and aiming in the general direction of where you normally sit with the laptop. It might be enuff to block a neighbors cordless phone signal by making it more directional. If that's the cause. Or simply move the router somewhere a bit different. Small moves can make a big difference on signal strengths.

Maybe get an idea here...
http://www.freeantennas.com/projects/Ez-10/

I've quickly made some with a $2 Styrofoam cooler and $2 worth of alum roof valley flashing from hardware store. And some clear 2 inch packing tape. Don't have to be real exact dimensions to work just fine - unless you really do need some most perfect signal boost.

Just a quick afterthought.. have you checked to see what wifi signal channels are used in your immediate area ? Your neighbors wifi.
If you and neighbor are on same channel or just separated by a couple channels... you will see some stalls when he moves bytes. Frequency will be busy.

Channel separation is important,,, channel 1, 6, 11 are each as far apart from each other as possible.

Yeah, that's the one thing we did try already -- switched from the default (channel 6) to channel 11. There's one other network that I can see, and that's it. I live around a bunch of old fogies...they don't know about the Intertubes. ;)

You can try making a reflector for your routers antenna and aiming in the general direction of where you normally sit with the laptop.

I'm really less concerned about the laptop, and more concerned about the regular computers. They are NOT wireless, but hardwired (is that the right term?) to the router. Those are the computers we play online games on, and that's the real annoyance when the connection drops. Will your reflector idea do anything for that?

Maybe twist your antenna down and put a pie pan over it while you play a couple games... so effectively it cant recieve a signal... then maybe you might know if its wifi or phone interference causing the router to reset the connection.

If your neighbors wifi or phone is causing the router problem, with a reflector you might get lucky and make ur signal to them weaker or invisible.