mildiner86 :
Dont u mean Partitions, as u should be able to have xp and 7 on the same physical drive just make sure u partition it
looks like the editing didnt work, i also wanted to add to my original message that each windows-installation has to be on a different HD or partition
pros for 2 HD: if one HD crashes, you can still start up the other one
cons: you need 2 drives: more costly and less room in the case left for other HD's
pros for 2 partitions: 1 HD needed, you can use a small drive just for programs, other drives for data
cons: if the HD crashes, you lose both installations (if the windows-installation got bugged, you can still use the other one)
personally i use 2 partitions on one HD for the installations and other HD's for all my data(including my docs, desktop, mails)