You can also use "The Ultimate BootCD" (approx 100MB Dl, I think) to boot the PC and use the included utils to wipe the partitions & set them up as you want
Or you can just run the Suse 10.2 linux installer (or Live CD) which will let you trash the HD partitions as you wish. - But it's a 4GB download
WinXP will fix up the MBR, as it needs, upon installation, no matter what vista tricks are happening, and will format the partitions clean
The bios is not accessible by Vista or Winxp. The bios just sets the first (boot) drive, and tells the CPU to request the first sectors of the (boot) drive, which is the MBR.
If you have multiple HD's, you can use multiple MBR's & install one OS on one drive & another OS on another (or let Vista/Linux handle everything). Switching the boot/1st drive in the bios will make that HD active.
I've done both.
I have WinXP on the original HD. Then I've switched to another (boot) drive in the bios & installed SUSE linux.
Linux has conveniently picked up WinXP on the other drive also, but has installed the boot loader into the MBR of it's own HD, not the winXP drive.
If for any reason, the linux boot loader stops working, I can quickly change the boot order in bios & fire up WinXP from the original HD.
Vista should be the same as linux. Change the first/boot HD, install it & the MBR of the first/boot HD only will be affected, not every drive, which is a common misperception.
Be careful with SATA as you can use native SATA/PATA emulation which can confuse WinXP (and likely Vista too). Linux doesn't seem to care much and will boot regardless, but drive mounts can go awol, while they are still in the system