this is highly dependent on the bluetooth stack you use (i.e. software that came with your adapter). There are at least 4 of them I know
1. the microsoft one added in XP SP2 (not sure but this one may not support PAN at all)
2. widcomm stack
3. Toshiba stack
4. BlueSoleil stack

2. and 3. support PAN at least with recent versions but each is configured differently, never seen 4.

Since this is not specific to tablets so you may also search elsewhere and include you bt stack name. With widcomm try to google for 'widcomm PAN' or something similar.

Once you have it connected with your PC, you need to share your internet network connection with this (google for 'xp internet connection sharing').