Before you do anything make a system restore point to undo any vital
changes.
http://www.microsoft.com/windowsxp/using/helpandsupport/learnmore/systemrestore.mspx
After that.......
Download TuneUp Utilities 2006 (its free for 30 days) and use the StartUp
Manager that it contains.
http://www.tune-up.com/info/lp/tuneup-utilities/?ap=1646
It shows the app, the manufacturer and a "Trustworthiness" rating. You can
delete the entries or simply uncheck them to stop them from starting up. I
suggest you just uncheck the entries that you think you don't need. That
way, if you accidentally uncheck something you need, you can just start the
StartUp Manager and re-check it.
You can also try the free WinPatrol app at
http://www.snapfiles.com/reviews/WinPatrol/winpatrol.html. It shows you all
available info on the files/processes that start with your PC and shows
where the file is located on your hard drive. It does not uninstall the
app, but finding which app to uninstall should be rather easy with all of
the file and path info provided.
This is about as easy as it gets.
If you want to know what each file or entry does, there is an app called
WinTasks that will tell you that info for just about any file, but they do
not have a free version ($39 for Pro I think).
A freeware app that (although not an easy interface for a novice user due to
the huge amount of info thrown at you) that also will sow you online info
(program name, company name, etc.) for any running process is What's
Running. You can DL it at
http://www.snapfiles.com/reviews/Whats_Running/whatsrunning.html.
One of these should do the trick.