…Isn’t easy.  

I have an Adaptec AHA-2940 SCSI controller, which doesn’t have any drivers available on their support site for x64 systems.  I found them on a forum somewhere (perhaps not overly trust worthy): AdaptecAic78xx.  They have been taken from a Windows 7 x64 system apparently.

These aren’t signed, so you have to disable driver signing:

1. Hit the start button, power and then shift-click restart.  
2. Select “Troubleshoot”->“Advanced options”->“Windows Startup Settings”->restart.  
3. When the system starts up you get a selection of options.  Option 7 disables driver signing requirements.  

Then you can go to device manager, update the driver, go to “have disk” and select the folder extracted from the zip linked above.

The next bit isn’t all that intelligent, but works.  Go buy VueScan, it seems to have drivers for every scanner under the sun.