how to install Ubuntu and Windows XP in Mac

Hello there!
I have a intel based MacBook and installed Mac OS X 10.4.9. I have also installed Windows XP along with boot camp and both OS were working good. Now, I have installed Ubuntu 7.10 in third partition. Ubuntu was installed with one error like "unable to install boot loader". Any way, I finished the installation process. After that, I tried to boot Windows XP but that did not start. Moreover, I am not able to see the Ubuntu boot option when system boots. But, Mac is working good. What might be the problem? Is there any problem of 32/64 bit compatibility of Ubuntu with Mac.
I am worry about that. I have been trying since couple of days back. Waiting for your help.
Please.........

An Intel-based MacBook has almost the same hardware as a normal PC: an Intel Core 2 Duo processor, Intel chipset, Intel graphics chip, etc. There's no problem that has to do with 32- or 64-bitness. The 32-bit as well as the 64-bit version of Ubuntu should both work on a MacBook.

I don't have a MacBook myself, but you can find more info here:
https://help.ubuntu.com/community/MacBook