Roaming profiles not working between XPSP3 & XPSP2

[#1]

Hi all
We're in the midst of a desktop refresh project, migrating from XPSP2/Office2003 to XPSP3/Office2007.  As part of the process, the roaming profile path for all existing user accounts are updated to a new location, which has the desired effect of forcing the creation of a new profile for each user. 
1. However, once we configure a user's account & apps on their new machine, then log off and logon to an old machine (XPSP2) the "Personalized Settings" pop-up appears as if a new local account is being created but is listed as roaming profile in User Profiles (?!).  We've checked the user has the necessary permissions to their own roaming profile on the server.
2. Also, when the user logs off & logs on to their new machine again, they get a logon error about \...\cookies\index.dat being in use then another message about the local profile couldn't be found so a temp profile was created instead & got "Personalized Settings" pop-up again.  We discovered that rebooting instead of logging off resolved this second issue (I guess it must unload the index.dat file during shutdown, not logoff, which is a problem in itself).
So it appears users migrated to our new desktop (XPSP3) cannot 'roam' to an old desktop (XPSP2). 
Does anyone know why this is happening and what we could try to fix it please?

Thanks
Scott

[#2]

Hi Scott,
I'm not sure, but would suggest thinking about the following:
On the "old" machines, has the user previously logged into it before?  If so, the old profile might be cached.
Also, check the "old" machines are looking in the correct place for the root of the user profiles, I presume it gets that from AD, so I'm puzzled too.
I presume there's not an upgrade of the AD from 2003 to 2008 too, as I think this also affects the profile locations?