if third party assembled the ATI factory drivers that come on a regular OFFICIAL ATI installation CD DON"T work, you will get a warning at install. been there, done that
in XP, mine was recognized automatically, then i installed a 'borrowed' hydravision proggie to get the dual displays to have the the extended desktop rather than two of the same screens.
on the Radeon VE 64 meg dual head I got, everything reads ATI, but the installation CD is looking weird compared to ATI's. no hydravision included.
i actually ordered the installation CD from ATI after telling them I got the card second hand with no CD, cost $10 shipped from Canada.
baldy