50 processes really seems like a lot for Windows XP. When I first install windows xp, I usually have around 26 running, and right now, I have 31 after a couple months of use and with a few programs running, 50 is way too many. But unless one of those processes is spyware or something and is deliberately taking up processing time, I don't think that is going to slow down your computer as much as you are mentioning. One of my favorite sites for computer tweaks is the Black Viper super tweaks page http://www.blackviper.com/WinXP/supertweaks.htm
The website is pretty helpful in tweaking XP to work faster.