You cannot use the Message-Signaled Interrupts feature on a VIA processor when you use the current versions of Windows Vista and of Windows Server 2008
The current versions of Windows Vista and of Windows Server 2008 do not support the Message-Signaled Interrupts mechanism on a VIA processor. When you install the VIA processor, these operating systems cannot use the Message-Signaled Interrupts feature.
For example, you have both a VIA Nano CPU and an ATI PCI-E VGA card installed on a computer that is running Windows Vista. After you enter the system and you check the MSI Enable bit in the ATI PCI-E VGA card, you find that the bit is always set to 0 unexpectedly.
For more information on this issue, including potential causes, workarounds, and resolutions, see: Microsoft KB Article KB978331.