Most of what runs will be essential windows background tasks. That said, scan the lists for anything that isn't microsfot or windows, and search for that process using google. And take a look at your startup to see if there's anything loading that doesn't need to. Then maybe google a Win7 tweak guide, and try to figure out what you need and what you don't.
I was using a lite build of win 7 for a time - it ran really fast, but not having media player and not having task scheduler and not having heaps of other stuff, turned out to be a real pain in the long run.