oui dans ce cas je pense qu'il y a effectivement un bug sous vista pour l'instant

soit sous vista qui a du mal a gerer ca, soit dans un des 2 drv des cartes.
je regarde le lien de lone...
d'apres ce que je vois :
If multiple graphics adapters are present in a system, all of them must use the same WDDM driver. If there are two graphics adapters with WDDM drivers from two different manufacturers, then Windows will disable one of them. The VGA adapter will be enabled, and the second device will be disabled.
Notice that XPDM drivers still support heterogeneous multi-adapter as they did in Windows XP. A user who has such a configuration working fine in Windows XP will encounter a problem when upgrading to Windows Vista. An external monitor connected to one of the graphics adapters will have no video signal, because it is disabled. An error message will appear on system boot, as described later in this article.
The solution for this problem could be as follows:
• A user could force the installation of a XPDM driver for each of these devices, and therefore get heterogeneous multi-adapter multi-monitor to work as in Windows XP.
-Or-
• The user could change the graphics hardware configuration by choosing multiple graphics adapters that use the same WDDM driver. Graphics adapters from the same ASIC family generally have the same graphics driver. In late 2006, each of the major graphics vendors had a single WDDM driver for all supported WDDM graphics adapters. Please consult the graphics vendor's Web site for details on their driver support.
donc deja ca elimine la piste des drv generiques puisque tes cartes sont heterogenes, tu as donc absolument besoin des pilotes constructeur.
ensuite, comme ils disent, dans ton cas ca chie !!! essaye leur 1ere soluce a savoir de forcer l'install des drv pour xp et ca devrait passer. c'est pas tres propre mais bon, si ca marche... apres ca depend de ton utilisation, si tu bosses, s'il te manque dla perf c pas tres grave, c sur que si tu veux jouer ca devient difficile...
quant a la seconde solution : changer de carte ! tu m'as compris !!!!
les message d'erreur en bas du topic de lone a l'air d'etre le tien non ?
++