If you want to install Vista onto an XP computer, try the reverse tutorial: (XP already installed)
I'm not going to post any stats on XP, if you're running Vista, you certainly can run XP
*You will need your XP and Vista installation discs! Step 1 - Partition the Drive:
Vista comes with a nice partitioning tool, so i'll be using it instead of partition magic this time around.
-right-click computer under the start menu and choose "manage"
-right-click the drive you want to partition, and select "Shrink Partition"
-The amount you shrink the partition is the amount of space used for the XP partition, so i would suggest making it at least 3-
4GB in size, as a full XP installation will take 1.5GB on it's own.
-now right-click the unallocated memory and select new basic partition.
-Choose NTFS file system, this will save formatting before installation.
-name the drive anything you like, i chose "XP"
-click next on the rest of the screens and finish.
once the formatting is finished you will have something like this:
*this new partition is where your XP installation will go, so take note of it's location, in case there are multiple partitions
on the drive (there will now be atleast 2).