BleepingComputer.com: disable access

I have bought a computer a compaq pc with 2 gb ram and 500 gb hd.

I installed windows xp on c drive.

C = 40 gb
D = 40 gb
E = 380 gb
M= 40 gb

I installed windows 7 on drive M.

I will extract another 40 gb and will make a N drive on which i will install windows vista.

As windows 7 is a beta version, it may contain bugs and act as a threat to security of c, d and e drive.

I want to disable all kind of access to other drives from windows 7 primary drive i.e. M and windows vista primary drive i.e. N so that data no virus can affect dat in C, D and E drive.