xp isn't xp

old computer supposed to be xp home. Says so when I boot it.

New computer, one drive 64 bit vista, the other drive from the old computer.

The old xp won't boot so I tried to use my xp-pro disk to fix it. But
just says there is a partition with "Another system" on the drive... it
doesn't recognize it as xp and wants to delete it.

Any possibilities here?

From my 64 bit Vista drive is there a way to look at the old drive (as
slave) and find out what system is really on it?

Thanks
John