As an addition to the advice above, I use
http://www.answersthatwork.com/ to establish what I need running. There's a nice large alphabetised list of what is what that helps a lot.
I also use Starter from codestuff. It's a free startup manager with a simple interface. Download from -
http://members.lycos.co.uk/codestuff/
Also, I find StartUpMonitor -
http://www.mlin.net/StartupMonitor.shtml to be very very useful. It's tiny and runs permanently on your pc. Every time something wants to add itself to your startup list this program pops up and asks you first. Simple, free, and very effective.
