There are no Windows 7 drivers for any of the four 2448TA models. (Plus, Plus II, Pro and Pro II). Some people find that Windows Vista scanner drivers will work under Windows 7. Try downloading and installing the relevant driver from here:
http://www.mustek.com.tw/Support/
(Click 'Support', click on Be@rPaw', choose your printer from the drop-down menu. Unless you're sure that you're running the 64-bit version of Windows, select the 32-bit Vista driver).
Chris