With vista you can disable some services you do not use often or do not need to use
Here is link with the vista services, go dowdnl the list and disable ones you know you don't use or need, if you are not sure if you use it or not, leave it as is/
Hacking Windows Vista: Speeding Up the System Boot - OS, Software & Networking by ExtremeTech
Also, have you checked your startup folder to see what you have starting with the PC?
Click start, run, type msconfig and click the startup tab
Look at the startup tab and look down the list of programs that st\art with the PC and uncheck one you know you don't need to have started