|If it's a few years older than Windows 7 launch year (2009) you will probably be out of luck. Hardware manufacturer's don't like spending money on new drivers for old hardware, they would rather you bought new.|
Check the manufacturer's website. If they don't have a Windows 7 drivers for it you can stop looking because you won't find it anywhere else.
In case you're out of luck, VueScan software may allow your scanner to function on Windows 7. Download the trial here: http://www.hamrick.com/
If it works you can then decide whether to pay for a registration code or buy a new scanner.