OS-X Tiger:

1. open system-preferences.
2. click on print & fax.
3. click on + to add a new printer.
4. wait.
5. click on More Printers...
6. click on the top drop-down box, and select "Windows Printing".
7. click on the second drop-down box (just below), select "Network Neighborhood".
8. hunt for your WinXP box and printer.

Good luck.