Problem trying to delete one partition with OS

[zaza]

I have this media center PC, it has 2 partitions, one has a new install of XP Pro on it, and the other Media Center. Now, I re-installed MC on it, and have to choose which OS I want to boot, so okay, I boot MC, and on the desktop I think all I have to do is just right click on Local Disk J which has Pro on it, and format, but it says something about set up files, and won't let me delete it. So, I think alright, I'll boot my own copy of xp pro, and then delete the original OS through the installation, but I do that, and for some strange reason, it leaves Pro on there, and kills my copy of MC, so, I can obviously re-install MC, and use the key on the back, but I can't leave it with Pro on it, because that key belongs to me, and I need to sell this PC.

Not sure of what to do. It just will not let me remove the XP Pro partition..

 

[zaza]

thing is, I can't delete the partition with Pro on it from the blue installation screen, I get the same message, contains setup files or something. So, simply won't work by the looks of things. What's other options do I have?