Use XP's Disc Management to view the properties of the partition, and possibly delete it and create a new one in it's place.

Or delete all (you'll lose the data that's on it, so copy that to a safe place before you do it) and create 1 big partition.

Or buy a program like Partition Magic and use that to edit the partitions while keeping your data (with 99% certainty).

Totally your choice.