Most of the USB scannes Drivers you'll be able to get from manufacturer's site. Just Download and setup - all USB products are Plung and Play. It will automatically recognise and install. You should however your scanner model number ready with you.
The second option is - most of the popular scanners have compatible USB drivers in Windows XP programmes upwards. ot this, just connect your scanner through USB post to your comp. Connect power cord. It will show, New hardware found. If it asks for XP CD, your driver is windows itself.
Third option is, repeat he process as described in No 2 - and install a TWAIIN driver, which comes with all Photo programmes, as well Windows XP. This should also be able to run your scanner
I hope one of these will be able to solve your problem. If not, contact the manufacturer's/dealer's local office/help centre