XP/Vista Dual Boot process doesn't complete

William,
I Followed the directions to the letter and got a message that said I couldn't partition the hard drive because it already had all the partitions it could take. Why did I think this was going to be easy?

Here's the config of my Dell computer in Computer Management:
Volume (blank)
layout simple
type Basic
file system (blank)
status Healthy (EISA configuration)

Volume (blank)
layout simple
type Basic
file system (blank)
status Healthy (primary)

Volume OS (C)
layout simple
type Basic
file system NTFS
status Healthy (System, Boot, Page File, Active, Crash Dump, Primary

Volume RECOVERY (D)
layout simple
type NTFS
File system NTFS
status Healthy (Primary Partition)

Bottom 6 windows appear as follows:
1. Disk 0 Basic 298.09 GB Online

2. 86 MB Healthy
3. RECOVERY (D) 10.00 GB NTFS helathy (Primary)
4. OS (C) 261.02 GB NTFS Healthy (System, Boot, page file, active, crash dump, primary
5. 24.48 GB unallocated (I think I did this when I chose the new simple volume and specified volume size much larger than I should have) --Now it won't let me undo this.
6. 2.50 GB Healthy (Primary)