I installed Ubuntu along side windows xp, and at the choose OS screen my keyboard doesn't work. I can't even hit enter to just start xp I have to wait for the count down. Any ideas?
You're probably using a USB keyboard on an at least somewhat old machine. Usually that works fine, but occasionally it doesn't.
A similar problem was encountered several months ago. This problem almost certainly is with your hardware (USB controller and/or keyboard), and/or your BIOS, and neither with Ubuntu (the OS you're trying to boot, but which is never actually running yet) nor Windows (which provides the boot menu that's not working...but is unlikely to be responsible for the problem).
Here are some things you can try:
(1) Enable legacy mode (for USB) in your BIOS setup (if it has that, and it's disabled). You can try disabling it if it's enabled, though that's considerably less likely to help.
(2) Install a BIOS update, if there is one available.
(3) If this is a USB keyboard plugged into the front (or top) of your machine, you could try plugging it into a USB port on the back of your machine. This will probably not help, but it's possible that some USB ports (the lower-numbered ones, which are usually on the back) work better for the simple I/O that is being used before an OS is booted.
(4) Try a different keyboard. Specifically, if this is a USB keyboard (which it almost certainly is), try a PS/2 keyboard. (It seems unlikely that this is a PS/2 keyboard, but if it is, try a USB keyboard.) This is the most likely to help.