Installer differences - SQL2K under W2K versys W2K3

I'm doing an install for a proof-of-concept environment; the server I'm
installing to is W2K Sp4.

I have installed to several servers in this environment under the same
project, all of which are W2K3.

I used the same install binaries in each case.

For all the W2K3 servers, the install proceeds without a hitch - but in
the case of the W2K server, I'm being prompted for an install key. I
even copied the installer folder from one of the W2K3 servers to the
W2K server to confirm. The behavior is different. I'm logging into the
server with the same ID in each case, but it's a domain ID so I haven't
confirmed whether the ID has the same privs on each server.

I'm a bit confused. Any idea why the installer would prompt for a key
under one OS but not under another??

Thanks,

BD