short answer
http://www.glaryutilities.com/gu.html
but as with any tune-up utility, its limited in what it can do
long answer
Steps for making your computer faster:
1. uninstall any software you dont use regularly. Make sure you have as much free space on HD as - at least 20% free at all times.
2. if you have a lot of fonts you dont use (over 400) delete some, too many fonts can significantly slow down your machine
3. edit your startups: XP: start -> run -> msconfig-> startups. VISTA: Start -> search-> msconfig -> startups. Use the list at http://www.bleepingcomputer.com/startups to determine what can be safely removed. bear in mind that the results are case-sensitive so you need to match the capitalisation of the results from msconfig
4. look in your system tray and check to see if there is anything running you dont need. If there's anything there you can dispense with, edit its prefs by right clicking and telling it not to start when windws starts.
5. run http://www.glaryutilities.com/gu.html and tell it to fix registry issues
6. Make sure your windows installation is up to date from windowsupdate.com
7. run an antispyware scan. Superantispyware is very good, as is windows defender.
8. Disable visual effects, like Stardock in XP or Areo in Vista. Kill any transparencies or animation effects.
9. run an online virus scan to compliment the scanner you have on your machine. There is no virus detection software that has 100% detection rate. Its a good practice to do this periodically and to make sure your installed scanner is up to date.
http://www.eset.com/onlinescan/
http://www.kaspersky.com/virusscanner
10. defrag: XP: start -> programs -> accessories-> system tools-> disk defragmenter
11. right click your drives, properties ->tools-> error checking -> fix errors [reboot]
There is no 'magic solution' to a slow pc. The trick is regular maintenance and sensible use. Running too much software concurrently and irregular maintenance of your file system are usually the two main culprits.
Hope this helps. Happy computing...