Use your windows CD, boot from the CD. Then follow instruction to install Windows. Then you will hit the options for formation/deleting/partitioning. select your partition space you want to delete and the delete it. After that partition the space again. After that is done reformat it to whatever format you use i.e. FAT32/FAT/NTFS etc.. After that is done exit the setup.
You can also do it from inside windows as long as your not using anything that is on the partition. Simply go to my computer<select your partition and right click it<then go to the format option... It is pretty self explanitory at this point.