You have to use the fdisk command in DOS to accomplish this. Please be careful with this as a mistake could cause you to lose all data on all your drives. Even if you do it correctly, you will lose all data on your current D: drive (although your C: drive should not be affected). Lastly, the following is primarily from memory, as I can't test it without screwing up my own data.
Go to the MS Dos Prompt and type in fdisk <enter>. This should take you to a menu with several choices. Start by viewing your current partition information (option 4, I think). It should tell you that you have a Primary and an Extended partition and should also tell the sizes of each.
Next you want to delete your current logical drive in the Extended partition (this is where you'll lose the data on D

. Select option 3 from the main menu, and then option 3 from the next menu (Delete Logical Drive in the Extended Partition).
After you've deleted the logical drive, go back to the main menu (escape key). Now you want to recreate the logical drives. Choose option 1 (Create Partition or Logical Drive). Then choose option 3 (Create Logical Drive(s) in the extended partiion. You should get a choice about whether to use the whole partition or just part of it. You want to just use part of it (this will become your new D: drive). You can choose how much to use in percentages or in Megabytes. Make your selection and create the logical drive.
Then go back and do it again for the rest of the partition. This time you can just select the entire rest of the extended partition (i.e., 100%). This will become your E: drive. That should do it. Keep hitting escape until you exit fdisk, and close your DOS window.
You will now need to format the D: and E: drives. (Make sure you don't format your C: drive).
I think these are the correct steps. When doing it make sure you read everything on the screens - just in case I remembered things incorrectly. It's not very hard, but it is dangerous (from a destroying data standpoint).
Good luck. When you're finished your hard drive should now show three logical drives (C:, D:, and E:, and your CD-ROM's should follow that - F:, etc.).