Well, windoze simply assign the first disk it finds to c:, the next to d:, enz.
On your harrdisk (the psysical one) you should be able to find some jumpers that point to wether the harddisk is a 'master' or a 'slave'. If you have one disk, just expiriment with the jumpers,
and reboot. If windoze still thinks it's d:,
what's the problem ? Does it corrupt any of your programs ? it shouldn't.