Use drive with both XP and Win7

WD External Drives External Drives for PC
2

Maybe this will help 

http://wdc.custhelp.com/cgi-bin/wdc.cfg/php/enduser/std_adp.php?p_faqid=3865  I believe WD has a format tool and you need to select fast format and there is an option about XP if I remember right. Find your drive at WD and it shold be in the downloads.

Joe