I had the same problem with my gigabyte board when trying to install x64
vista this is the reply I got hope it helps:
When you are installing Vista x64 from media (DVD) that contains both
x86 and x64 versions you may get a misleading error message saying third
party drivers are unsigned. It is not incorrect.
If you are using combined 32/64 bit media for an install, the 32 bit
version of the Windows Preinstallation Environment (WPE) is always the
one that starts up initially. When you try to load the third party
drivers ("Load Drivers" option) and select the 64 bit drivers, the WPE
doesn't see any 32 bit drivers and pops up the message about the drivers
do not apply to your system or are unsigned.
To further confuse things WPE may see the 32 bit drivers if they are in
the same directory you specify as having the ones for x64. It will
silently load these drivers and display the target device. You can use
the partition and format tools so you think everything is OK. However,
when you select a partition and select next you get the drivers do not
apply or are unsigned message because the 32 bit WPE hands off the
install to the 64 bit WPE at that point.
1) The easiest solution is to use install media that is only for Vista
x64 (ISO images available for MSDN/TechNet subscribers). The 64 bit WPE
is always used.
2)Follow the instructions in the Microsoft Knowledge Base article
'How to install third-party mass storage drivers for the 64-bit
editions of Windows Server 2008 and of Windows Vista'
3) If you have USB stick, try to use USB stick to load driver.
4) We are wondering if you use purple GSATA ports or purple ports ? Use
yellow SATA port controlled by ICH chip instead of GSATA.
5) Are you using multi boot? since you are trying to install Vista 64,
but also mentions Vista 32 in first mail.
All so try these drivers: