What OS, what file system (FAT16/32, NTFS, etc)? How about the age of the BIOS - perhaps old enough that it can only support small partitions. That's about all that the FAT16 files system can support. FAT 32 can do larger.
And if you move the files, anything on what is now D will be on C so those pointers would have to be changed - possibly requiring some reinstall anyway. Partition Magic comes with Magic Mover to change the pointers for you - don't know of a freebie that does off hand.
There are lots of places that you can get PM8 for under $30. in the full OEM version - just froogle for it.
.bh.