Have you installed all the software that came with the camera?
Also make sure that the USB socket is working properly and that you're not getting conflicts.
Try a complete uninstall of camera software and reinstall - although XP should find it anyway.
Failing that, buy a memory card reader - they're fairly inexpensive and I find much faster than other methods.
I have an A70 and have never had any problems (so they do work with XP!)