Kentuck- I don't think a couple seconds spike to 99-100% is alarming. Mine does this occasionally when opening some programs or my browser. I think it's only an issue if you have a spike and it stays up there. For example, once in a while my Windows Media Player hangs up if I try to play a video at some sites and it ties up my computer at 100% until I go into the Task Manager and select it and shut it down. As for your question about what processes are essential, here is a link that lists the main background processes by their (sometimes inscrutable) names, and tells you what they do. Make sure you have the "Show processes from all users" box checked and compare the list of names. Some of the names you'll have will be processes specific to things like your antivirus, and won't be listed here. For those that aren't, just write the name down and do a Google search. (Sometimes a virus will show up in this list, although I don't think that's your problem.) As I write this, I have 53 processes in the background. I'd have more if I hadn't prevented things like RealPlayer and Quicktime from starting each time I bootup. Here is a link that might be useful: WinTasks Process Library

Slow at 2am would mean the computer is tired and needs rest... or you've had too much coffee maybe and your mind is speeding & that makes the computer seem slow. (kidding wiff ya ;) You might want to look at a program to defrag your registry called PageDefrag ... just type sysinternals into your browser, hold down the Control key and hit enter. Simple tiny program. There are other registry defrag programs for xp but a bit less effective. Do you manually defrag your hard drive occasionally ? A Fragged up hard drive slows things down, especially after a long day. Windows auto updates and virus scans seem to default to the wee hours of the morning to auto run ... that always worries me when I cant sleep. 'Whats that running my hard drive light' Those things running can make you slow down. ~~ I haven't personally messed with core selection. Really haven't read much about it but do understand how somebody at Microsoft says it works. In my mindset, I think you may be able to set programs CPU priority level probably more efficiently than trying to outsmart the way windows handles the core selection. Affinity on Xp, to change it permanently you will need a program to handle the settings. Windows will allow you to change core choice, but as soon as that program shuts down or at reboot, windows will revert to its default scheme of auto handling the cores... which from what I've read, windows does very well unless you have a program that for some reason gives you a hassle hogging both cores,,, or I guess if your computing habits are really stressing things making you think you can speed it up by slowing down a certain program, thus allowing one you want to do something 'right now' faster, yet at half speed, when that core is needed and shared elsewhere. Here is a link that might be useful: Toms Hdwe... old stuff but ,,, affinity.

1. Error Checking- This takes about 35 minutes. Start - my computer - right click local disk (C) - properties - Tools Tab - Error checking section - Check now - check mark both boxes - Start - This requires a restart to begin. Start - Run - type - sfc /scannow - OK Don't forget the space between c and / You may need the Recovery CD if any thing is found wrong. Don't insert unless asked for. Takes about 35 minutes. Disk Defragmenter Start - All Programs - Accessories - System Tools - Disk Defragmenter Or you can do as others have written.

I suggest she uninstall any unused programs and do a disk cleanup Start > Accessories > System Tools > Disk Cleanup. I use ccleaner but disk cleanup will get rid of some of the junk. She can then start the computer in safe mode by tapping the F8 key as the computer starts up. She will get a screen where she can choose to startup in safe mode. She can then right click on 'My Computer' click on 'Properties' click on the 'Tools' tab and check for errors by clicking 'Check Now' and then defrag by clicking 'Defragment Now'. This can be done without starting in safe mode but for someone who is new to the process I think this is the easiest way.