I have been unable to find driver on Acer website

Support Information:
Device Type: Scanner
Manufacturer: Acer
Model: Scan Prisa 640U
Interface: USB
Operating System: Windows XP Professional
Age of Device: < 2 years old
FCCID:

Find it on DriverGuide (http://members.driverguide.com/index.php?action=srch&sm=b&aax=&qa6=17&qa5=17&qa7=1500&dp=2&qm0=Scan+Prisa+640U&jmd=and&fzz=d) | Find it with Google (http://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=Acer+Scanner++Scan+Prisa+640U+Windows+XP+Profess ional+) | Research manufacturer Acer (http://members.driverguide.com/index.php?action=getinfo&companyid=17)

I didn't have any trouble finding it... in less than 30 seconds.

http://www.benq.us/support/downloads/downloads.cfm?product=85&page=downloads&dtype=D

Jerry the web address in your response isn't working

That's because the USA Benq website is down. I don't know if this is a temporary or permanent condition but you can click on the link below and select another country and probably find the driver. The post of mine above was posted over a year ago so it's possible the link has change but no link will work on the US website at the time of this post.

http://www.benq.com/support/