To find out what programs are loading on your PC at startup, you can run the Windows-resident system configuration utility called MSCONFIG. But there's another free utility called Autoruns that does the job better. MSCONFIG entries tend to be rather cryptic, for example, but Autoruns includes a line of description for each entry in plain English. Autoruns also lets you Hide Signed Microsoft Entries, which allows you to quickly narrow your focus to third-party programs. Disabling or deleting entries requires just one click (so you'll need to be careful!). This function really saved my sanity when my system was breached by a scrap of regenerative malware.
Autoruns is one of the Sysinternals utilities developed by Mark Russinovich and Bryce Cogswell. Somebody at Microsoft must have admired their work, because Microsoft bought the company last year and now touts these utilities from its own website.