Acer stopped manufacturing scanners quite a long time ago and the company no longer provides any drivers for them. They wouldn't have any Windows 7 drivers for them anyway, since Acer stopped making scanners long before Windows 7 was released.
You may want to try third-party software called VueScan
which supports USB scanners for which compatible drivers are not available:http://hamrick.com
Install the trial version. If it works with your scanner you can either pay for a registration key to keep using it ($40 US Dollars), or buy a new scanner. It's your choice.