Definately permission's
Make sure both are in the same workgroup
Then make sure that both machines have the same account names and passwords on both. Then try again.
Its really not a good idea to run with no passwords on accounts. Make sure as well that the XP machine has a admin account and a basic user account always use the user account for day to day running.
Also as well its better to create a saperate share for each drive or point of data on the DT. Then map a drive to each of those.