lost 8gb drive space on D:

first hard drive is a seagate 10 gig with C:\ win 98 se. second drive D: is a maxtor 15 gig. I had win xp pro and l partitioned 8 gigs for linux Mandrake 8.1. I got a poor installation so I formated D: from C: erased xp pro fine but lost the space Iassigned for mandrake how can I reformat the intire drive and start over with 15 gigs.