The OpticPro A3I is not Windows 7 compatible. (It wasn't compatible with Windows XP and they did not add support for the newer OS.) The OpticPro A320 and A360 are compatible with Windows 7. Support for the newest OpticPro A3 models is available here: http://plustek.com/usa/products/opticpro-a3-series/
If you have one of the other models in the series, please let me know. I suspect the OptiPro A3-U will be best under Windows XP in a dual boot, stand-alone or virtual computer.
You can run an XP virtual computer for free with Windows 7 Pro or Ultimate. Download and install Microsoft's Virtual PC and XP mode. Then install the scanner to the XP mode as if you are using a normal XP computer. The other options require a licensed version of XP. Virtual computers have one issue; they can not share files with the main computer directly. You will need to save files to external media (CD or flash drive) to transfer them.
I hope this helps.