If you have a Windows XP CD you can boot with the CD and use the installation program to delete the hidden partition. After you delete it just quit the installation (F3 key). Then use disk management to format the 5 gigs.
Tip: Before you do this, rename BOTH of your hard drives in My Computer to something like HDD1 & HDD2. Then delete the one that you didn’t rename (because it was hidden).
If you don’t have a Windows CD, you can still delete it but you must use the command console [DOS for XP].