I goofed up today and ended up not being able to boot up my laptop. And I'd like to write down what I did here for future reference:
1 Insert xp installation disk
2 Three options are available:
a/Install windows
b/Repair windows
c/Exit
3 choose option 2
4 enter administrator password
5 choose which OS to repair; hit enter
6 type HELP
7 or type fixboot
8 then type fixmbr
It worked!!!