Disk Error after trying to start on Windows OS

I just tried to install Windows XP on Bootcamp. I think I had a corrupt hal.dll file or something, but for some reason, the computer said that it was a successful installation. So i ejected the disk after it restarted, went to system preferences, and restarted the computer on the Windows OS. After going to a white screen, it turned black and all it shows right now is:

"Disk error
Press any key to restart
_"

Main problem right now: I can't switch back to Mac OS. And the Windows OS is stuck on the black screen.

The command "Press any key to restart" doesn't work. Neither does the "hold down option key during startup." I've tried to re-install the OS using the Windows disk again, but that didn't work either. Same with Restore system disc and press C. It always ends up on the black screen with the message.

Any suggestions please?

Currently using another computer to post this.

You need to hold the option key down until you get to the boot menu (not just press it).

If you are doing that, then it sounds like you have installed windows over your OS X partition instead of the BootCamp partition.

If this is the case, it's time to reach for your OS X discs for a reinstall.