Hi there
I had that problem with my copy, and there IS a way around, it's a little tricky but I'm running a dual Athlon MP1900+ w/ WXP and RAT 4.5 PERFECTLY w/ no hangs or nothing like that....
Well the secret is .....
When you're installing the licence server you have to press the cancel button just a moment before it rolls back and uninstall every thing.
This ways all the files are still in the Program Files/Pixar/License Directory, copy that directory to another folder, and also copy the registry (w/ registry editor) named pixar license server to a .REG output file.
Then cancel the installation of the license server re-copy that directory you had copied to other location into the proper license directory, add the .REG file to your registry, restart the computer, load maya load prman
and have Phun....
Kinda tricky huh?
but worked for me....
just to let you all know that RAT4.5 does work on XP.
Best Regards...
[THE]Shadowman
"For we are many........."