I suggest getting this program to see what excately is starting up when your computer starts up. You can just disable stuff you do not want to start on startup and see what happens from there:
http://www.mlin.net/StartupCPL.shtml
My guess is that many programs are running on startup causing the system to slow down. I'd figure once you disable any programs you do not want to load on startup, then your system should be okay!