@virus, use a temporary drive!

jus the programming logic,
suppose there r C,D,E drives and they got changed to C E F and D drive has become say anotehr hardisk partition... now change D to say X, D->X, E->D, F->E, X->G or watever...
@g_goyal2000, windows makes sure that the primary of every hardisk comes first. so C drive is ur first hardisk primary and D drive is the secondary of ur first.. when u installed second hardisk it jus has changed it back. u can always change the drive letters permanently until next installation atleast using the method told by arun.
/legolas