While I understand your apprehension about doing a fresh install of Windows 7, that will probably give you the best results when compared to using several utilities to improve the performance. It will also give you the opportunity to only install programs and services that you really need and nothing more.
Also, before you do the fresh install, you might want to consider opening up your PC case, disassembling the components, giving them a good cleanup and putting them back together. Clean hardware in a well ventilated case solves a no. of heat related problems.
Anyway, if you would still like to clean out the crap from your computer, consider a program like CCleaner to remove junk files.
EDIT: Yep, follow Allan's suggestion to use the MSCONFIG utility to improve your start up speed.
Hope this helps.
Edited by ReviverSoft, 20 April 2012 - 07:56 AM.