format help

Ok, I'm a newbie and I did something silly
I'm running WinXP pro, and I accidently installed it twice on 2 different partitions. I tried formating from the command prompt in safe mode got a message that formating was not allowed on that drive. I thought about using the XP disc to format the drive, but I don't want to reinstall windows again to that drive since I'm already running it on another drive partition.
Any ideas?

 

Boot to the OS or partition you want to keep, then go to:
control pannel:
Administrative tools:
Computer management:
Disk management:
Then right click on the partition/os that you dont want, and then click on format, follow prompts

 

I followed the prompts in my disk manager, but "format" is not an option on this drive. On another partition that does not have a windows installation on it, "format" comes up as an option. The drive I want to keep (e) comes up as "healthy (boot)", while the drive I want to format (c) comes up as "healthy (system).
I don't know if this matters, but the one I'm trying to format comes up as a primary partition, while the other two (including the one I booted to) come up as extended partition.