Error 18

I've been looking around and it seems that most users encounter this problem when they are installing ubuntu and windows to the same harddrive. I've had my comp running dual OS for almost a year with no problems and then this morning my laptop suddenly froze while playing music and the following reboot prompted the "grub loading error 18". It's a shitty top but Ubuntu runs great on it.

(Presario V2000, AMD Turion 64 Mobile, 1800MHz with 512MB system memory, PhoenixBIOS F.21).

I'm at a complete loss. I lent out my ubuntu disk to a friend and can't get another for a while. I also can't find my windows XP install disk which I'm sure is around here somewhere. I hate to be so nooby but I have to present a seminar on Monday and without my top I'll be forced to work on it all at school..which would suck the big one. Also .. It's never cool not to have a working computa. Any help is greatly appreciated.