Given your apparent lack of experience with dual booting configurations I'm
going to suggest you reconsider.
I'll tell you why.
First of all, Windows XP causes some potentially serious issues when
coexisting on a system with Windows Vista in that it will actively sabotage
the restore points set by the Vista system for its own use. There are ways
around this (namely by using one technique or another to hide the Vista
installation from the Windows XP installation), but they will involve either
a change in the version of Vista you are using to the much more expensive
Ultimate version (along with a fairly complex procedure) or use of a third
party partitioner / boot manager. If you don't care about restore points for
Vista, then I guess this issue doesn't matter. Just turn of system restore on
the Vista installation in that case.
As a second point, what flambe says about the boot record on your C: drive
is also true. What that means is that if / when you decide to get rid of
Vista, you will still be left with the Vista boot loader on your Windows XP
drive. (And don't even think about trying to install Vista on the first hard
drive and XP o nthe second one. It can be done, but it isn't for the faint of
heart.)
That being said, if you wish to proceed, there is another way to dual boot.
If you can change the boto drive order in your BIOS you can set the system so
that the second drive is drive C:, install Vista on it, then use the BIOS to
give you the choice about which OS you will be booting from when you start or
restart the computer. This sounds simple, but you do have to understand
exactly what you're doing in order to use this method.
Finally, if the system has enough RAM and speed, you might want to consider
the possibility of installing one operating system as the primary operating
system and the other operating system on a virtual machine (probably under
Virtual PC, a free download from Microsoft). This gives you the advantage of
being able to boot into one operating system and switch to the other
operating system without rebooting.
If you want to consider the virtual machine route you have to decide which
operating system needs the most direct hardware support. If you are keeping
WinXP MCE primarily for its hardware / software support of your system, then
you want to make it your primary operating system and run Vista in the
virtual machine.
You will need a lot of memory (at least 2 gigabytes, which you may well have
on that system) to do this with any expectation of decent performance on the
virtual machine.
Any of these approaches has advantages and disadvantages too numerous to be
listed in a reasonable fashion in a message thread.
