Dual-Boot
I have "triple-boot".
I have two HDs: 320Gb, partitioned to 20Gb > C:, 300Gb >D. This drive has my Windows XP Pro on it.
I added another HD: 500Gb. which I partitioned 22Gb > C:, 460Gb > D:, 24Gb > E:
After installing Vista on my "C:" partition on 500Gb., I ended up with dual-boot. Then I installed Win7 on E: (24Gb)
When I re-booted, I ended up with Triple-Boot.
Windows is always on C: irrespective of the partition or drive. The rest of the Drive letters alter with each different boot.
I used BCDedit to edit my triple boot so that Win7 is 1st, Vista is 2nd & XP 3rd.