Try doing theses things on this page: http://www.microsoft.com/atwork/maintenance/speed.aspx
After that try CCleaner. I use it everyday to keep my computer clean and it’s FREE! Go here for the free download: http://www.snapfiles.com/reviews/CCleaner/ccleaner.html
CCleaner also allows you to stop/start loading programs, but I don't think it's available at this very moment.
I got Webroot’s Window Washer years ago and it’s terrific.