Moving the OS safely

I have three hard drives.
An 18 gig as the master;an 80gig as a slave and a 200gig as another slave.
I keep getting the message now that there is insufficient space on my master hard drive and I still have a lot of space on my slave drives.
How do I move the OS to my 80gig drive without causing systems problems, please ?
I suspect just a straight file move across from one disk to another won't do it.

Cirdan

You would need to change the 80 to Master and reinstall XP.

You might be able to use the install utility of the drive manufacturer to clone the drive if for some reason you do not want to reinstall clean.

You could also just move non-program files off of the 18 for more room.

Thank you jephree, I will give it a go.
I have alreadt moved non-program files off the 18 but that was insufficient for space.

Cirdan