I also had same kind of problem I changed the USB cable it worked. (the old cable works with the other computers but not with this one). I did lot of googling about this problem some time back. Its a problem with the XP. Even in Microsofts site I saw some advices regarding this kind of problem. It seems that they have not solved these kind of problems yet (I read somewhere).
Now my Sony Micro Vault (Pen Drive) is not recognised in my system

. I don't know what to do for that

. Mad Mad XP. I am fed up with these USB things now, I stopped using my sony micro vault.