Non-responsive Keyboard

Interesting problem, I've had a few problems for a while now to do with the keyboard on my Mac, things like it acting as if I am constantly holding down the ¨t¨ key.
However now I have a new one, simple...ish. When I boot into OS X 10.5.5, most of the keyboard doesn't work, the function buttons work, changing the brightness, volume, eject, etc. Some of the buttons at the bottom of the board work, I can activate Spotlight with command+spacebar, however I cannot type anything, and if I open Firefox and begin typing, it freezes and almost instantly runs Firefox crash reporter!
Strange thing is the whole thing works in a boot camp Windows XP, SP3, on a partition. I'm using it to type this post!
I've tried PRAM/NVRAM and an SMC reset to no avail.
Any ideas anyone? Anything at all would be greatly appreciated!

Thanks
Jamie