How to boot ubuntu 10.10 from windows?

I installed ubuntu 10.10 on my computer using the installer that you can just download and let run.
However, when the installer was finished, and I rebooted my computer, there was a screen that said to use the arrow keys to highlight which boot option to use. But the arrow keys won't register, so the selection stays on win xp. I also tried pressing num lock a bunch of times and using the arrow keys on the number pad, but it doesn't work. Is there any way to run ubuntu directly from windows using an ms-dos command? Or how am I supposed to boot it?
Thanks for any help.

USB keyboard?

Have you by any chance got a USB keyboard. If you have and it is not working the answer lies in your BIOS and not in Ubuntu. If you have a USB keyboard can you try a PS/2 instead ?