You have to boot the Windows 7 installation DVD to use diskpart to do the clean all, it can't be done from within Windows; have a look at Method One of this tutorial.
Thankyou thankyou thankyou, my old girls working as good as new on windows 7, everything is working great. HEAVEN. Numpty here just put disc in wrong disc drive at start, but as for the rest, wasnt half as bad as i thought.
So a BIG BIG THANKYOU 2 all you guys your ace.
Thanks Jenny