Jeez Slinky :
160 GB HDD.

I wouldn't worry about losing a MB or two
Seriously, it's better to just get the partitions done and dusted, and get down to some quality PC time

I'm running with two 40GB HDD's.
One is for dual boot Win2KPro / XPPro + data.
Other is for images of each OS, plus music and a couple of games, and I've got a heap of GB left over, you can have them if you want