3 years ... it neds re-building if you can put up with the hassle ...
I do mine 12-18 months.
even with low use it's surprising the ammount of rubbish that collects.
you could clean out the temp folder (that's where most collects) - I assume XP?
to clean the temp folder
copy this lot between the ****s (not the ****s)to a notepad TXT file
********************
echo off
rd /s /q %temp%\
del /q %temp%\*.*
pause
*********************
save the file as tmpcln.bat on your desktop
double click ... and you'll see the results.
If it's 3 years old .... I'm guessing a 2-3 Ghz p4 with 128- 256 ram?
if xp 512 is a good number 1Gb is even better (www.crucial.com - run the checker)
98 will fly with half that.
if you have the time a rebuild will make a big difference (add extra ram and you'll be amazed )
before you start however .... make sure you have all the CDs that came with the machine (without drivers you've got problems)
or back them up using
http://www.innovative-sol.com/drivermax/ (it's free)
before you start