In XP I also had to not only enable shareing of the folder, but I had to modify the permisions in the same file shareing tab there should be a button. I added my mothers account and then had to give it read and write permisions. This permisions option only becomes available in XP after turning off simple file shareing in folder options I think it was

This was the only way I was able to let her have full access to her files.

Maybe this can help you.