There are a lot of extra extensions that you could turn off that could increase system performance. If your using a printer turn on only the extension needed for your printer,and turn off all the rest(or turn them all off if your not using a printer). If your not on a network, you can turn off all of those extensions. Turn off any non-internet extensions i.e if your not using AOL etc...
Bottom line though, your gonna have to go through your extensions one at a time to see what you can and can't turn off.
Make sure to keep Virtual Memory turned off, it's murder on your system, I've noticed.