Basically, you can start by using msconfig (Start|Run|"msconfig") same as in 98. That will let you see what is running at startup and such. From there, it comes down to disabling services that you don't use. Some will be obvious, and some will not. Use the Services applet in Administrative Tools from the Start menu. Turn off the obvious ones, and ask questions here about the rest. I've got mine pretty tweaked down as it is.
Lephturn