AFAIK-
The profile is usually C:\Documents and Settings\<username>\NTUSER.DAT
With roaming profiles, you identify the location of this file with 
various [NETLOGON] and [GLOBAL] settings.  It is copied into the 
C:\Documents and Settings\<username>\NTUSER.DAT on login and copied back 
to the server location on logout.  Everything else can be redirected.
Profiles can be shared between NT and Win2K.  I don't know about XP.  If 
you have users who move between different architectures, you can use the 
%a variable to identify the OS and select the appropriate profile to load.
I hope that is close.
Michael
Adrian told me on 12/14/2005 00:23:> What exactly comprises a profile? Do they have anything more than the
> contents of a user's "Documents and Settings" directory?
> 
> To what extent is profile data shared between Windows OSes?
> 
> Thanks.