http://support.acer.com/answers.aspx
The above is the support line for acer, but I don't think you want to call it just yet, as it is very expensive.
I could not locate a driver for your acer w4300u flatbed scanner as they don't list it on their website, even categorically, there are no scanners listed on their website.
However, there are aftermarket resource on the Internet such as the following:
http://members.driverguide.com/driver/detail.php?driverid=1386363
I read that Acer may have changed their name to Benq, so look for that driver and also Windows Vista or XP is the highest that is supported, but Windows 7 may have drivers when it tries to install with an Internet connection present, or be able to use the older Legacy drivers.
I wish you luck on this installation of a w4300u flatbed scanner.