Are they on seperate drives?
if they are on seperate drives. (eg c: & d
than load up the windows you wish to keep loaded. and enter MS-DOS
Through ms-dos you can format the 2nd drive (this is not recommended if you have any personal files on the drive... move the files to the o/s which you are keeping)
if your windows o/s that you are keeping is on DRIVE C:
In the MS-DOS prompt you should see:
C:\WINDOWS\
type .. FORMAT (drive letter to be formatted):
(eg. FORMAT D
This will prompt the format disk tool, which will run you through the rest.
Hope that helps, ciao.