This calls for a re-format. If this is the system drive, windows should give you an option to format the drive somewhere in the install process. If it is just a data drive (i.e., without windows) you should be able to format it from the disk management utility. Right click on the drive and there should be the option. I think that if you right click on the drive in My Computer it might also give you the format option, but I'm not sure.
I just want to get rid of the info that is on there and put vista ultimate on the drive