gep--Ah, ha. Another victim for my canned suggestions.

"1) Disk Cleanup. There are several ways to reach it. One is Start|All Programs|Accessories|System Tools|DiskCleanUp. That will start a scan of the PC to tell you what files might be deleted or compressed. (The scan takes a while.) I would certainly delete Temporary Internet Files, Temp files, Downloaded Program Files and probably Compress Old Files. See http://support.microsoft.com/kb/310312 for details.
2) Then I would run ErrorChecking. (left click on MyComputer||right click on C:\ drive icon (assuming that is your hard drive)|Tools|Error Checking. Check the box "Automatically fix file system errors". Click Start (within the error checking window). You will be told to reboot. Do so. Error checking will then run as part of the reboot. It can take a while.
3) Start|Run|type MSCONFIG|OK|Startup tab. WinXP actually needs very few thirdparty programs (the ones you see in msconfig) to run at start. Antivirus, Firewall, Antispyware, programs associated with wireless connections such as mouse, network, etc. would be among the few. Uncheck the box to the left of any program you feel you do not need at startup. Click Apply. This site will help you make decisions what you do and do not need http://www.sysinfo.org/startuplist.php
4) Run Disk Defragmenter. ((left click on MyComputer||right click on C:\ drive icon (again assuming that is your hard drive)|Tools|Disk Defragmenter|Defrag Now click Analyze) Unless the analysis shows defragmentation is not needed, proceed to run Defragment. That also takes a while."