If you're looking to manually track down spyware, or speed up system startup--and you're a technically astute user who's comfortable with Registry settings--then the free RunAlyzer may be just what you need. Run it, and it performs a thorough and sophisticated analysis of all programs and services that run when you start up your computer, and shows you details about each, down to the actual Registry settings that launch or control them. Based on what you find, you can (if you're technically sophisticated enough) determine whether suspicious programs are running, and you can also speed up startup by stopping unnecessary programs from running.
As the hints above suggest, this is not software for the novice or even intermediate user. You won't get much help interpreting what you see. Instead, you'll get a list of all programs in your Startup folder, and be shown the Registry keys used to start or control programs that launch on startup. You then have to determine on your own whether the programs are necessary or not--or dangerous--and take action. RunAlyzer includes tools for making changes to startup, such as editing Registry keys, or toggling Registry settings on and off.
That's not to say that you're completely on your own. You can have the software send your startup information to a site run by RunALyzer's maker, Safer Networking, and you'll get an analysis of what it finds. This is particularly useful if you suspect you're the victim of spyware. Safer Networking also makes the popular anti-spyware software Spybot Search & Destroy.
There's plenty more to RunAlyzer. It also shows you tasks scheduled to run, displays information about Internet Explorer plug-ins, and more. The technically sophisticated will welcome this program with open arms. Others may be merely baffled.