If you are using that drive as a slave, you should be able to do the following:
- Open the Control Panel
- Open Administrative Tools
- Open Computer Management
- Under the Storage node on the left side, select 'Disk Management'
- Find the drive/partition you want to 'fdisk', and right click it and select "Delete Parition..."
Anyone familiar enough to even look for fdisk should be able to make out what Microsoft was doing with this Logical Disk Manager thingy. Basically a fdisk GUI.