Alex, yes you can control what start up on your computer. This has alot of affect on slow computers. You'll probably be amazed what you will find starting up. This is how you do it on Windows XP's.
Start
Run
Then type MSCONFIG
Then look at your folders, and find START UP.
Anything that is clicket obviously is enabled. Becareful what you unclick, i know my current computer inside out. Most people dont, so be careful. Also, i do agree on 1GB RAM upgrade.