Change boot drive from D: to C: where partitions are on same drive

I have a new system which came with C primary partition and a D logical drive on the same disk. I lost my registry, couldn’t boot and couldn’t recover, so reinstalled XP and programs onto the D drive (to ensure I could recover all files etc on C).

Now everything is fine, can I delete the contents of C and transfer everything back from D? The reason is C is bigger and the original D was intended for back up (hadn’t got round to it!). File system is NTFS.

I do not want to have to reinstal everything again.