Hi, Andrew.
Sounds like you've never actually tried this. So long as they are in
separate volumes (primary partitions or logical drives in an extended
partition) there is no problem. I've had three versions of Windows running
in three logical drives in one extended partition. Each volume, of course,
has a separate "drive" letter, so I had MS-DOS in Drive C: (a primary
partition), plus Win98 in D:\Windows, Win2K in E:\WinNT, plus WinXP in
X:\Windows. No, wait, X: was a logical drive on a second HD. Right now I
still have MS-DOS in C:, and WinXP in D: on the first HD; WinXP (different
license number) in X: on the second drive, and Windows Server 2003 and
Longhorn (PDC version) in separate logical drives on the third HD. And I
did have two copies of the same license installed for a while until someone
suggested it might not be legal. As Rick said, both copies activated
without a problem.
But I've never been brave enough to put two Windows installations in the
same volume.
As to the legality of multiple copies of the same WinXP license on the same
computer: I've read the EULA and it sounds ambiguous to me. I've asked in
a few newsgroups and had no definitive answers. My gut feeling is that
there should be no problem. I could never be booted into both copies at
once, and this IS the same computer, so I see no way that MS is being
harmed. And a second installation comes in mighty handy sometimes for
repairs to the first installation, like editing bad Registry hives - which
is what got me into dual-booting in the first place a few years ago with
WinNT4. I don't speak for Microsoft, of course, so this opinion is just
mine, and not official at all.
RC