Have you checked to see if your Internet Service has
parental controls? AOL has these controls. You can block some websites with your host file but it would be hard to get them all.
You can set up a limited account for your computer. That would mean everyone would have to have a password to open your computer.
You can go to Internet Options in the Control Panel to set
limits on what is view on your computer. Anyone with Administrator right can change them. So kids would have to have a password for a limited account.
If I'm wrong someone will let you know.

I found the site below. Would it be safe to download? I just want to block social networking sites on my computer, but I don't want to make it difficult for me to navigate.

http://www.opendns.com/

Circumventing parental controls is not rocket surgery to
kids today.
If your child, and I assume it's your child you're concerned about, wants to bypass a blocker they'll
find a way...and there are several.
They either have the know-how or they'll have a friend who knows how.
They can also Google for instructions.
I don't want to lick the red off your apple but no blocker
is geared to "set it and forget it".

Put your computer in a high traffic area of the house and
try education and trust..with well defined consequences if
that trust is broken.

One thing you need to do is set the PC monitor in an area where you can see it when you walk past the room, or better yet put it in the family room or any room where people are in and out all the time. My cousin volunteered at a public library and she said the kids would come in and look at porn on the computers. I told her to turn them around so the monitors face the front desk, very simple. She said that is an invasion of their privacy. Unbelievable.

this is one that you can find a ton of info on using google.
The first one on top gives great info.

If you do not have them set up on limited user accounts that are locked down that is the first step.

Here is a link that might be useful: xp parental controls

www.opendns.org is safe - been around for a long time.
I forget if the 'Free' membership has domain blocking or not.

It simply new dns server settings. They have several nice features and its Quick !