I would also suggest running a few utilities through the system to check it over. Start-up Cop will check anything that starts when you switch on, and give a hint as to what it does and if its needed.

Then find a good spy-bot, there are loads and everyone is different so search for a good one. I use SPYBOT Search and Destroy 1.3 again this will check for things that really shouldnt be there type of thing!!