primary mirrored disk failure

We have a server, nt server 4.0 sp 5, that has it’s boot partitioned mirrored on two fat drives. The original drive is having memory problems, so we want to replace it with a new one. We broke the mirror, and the primary drive is now assigned letter c: and the secondary is e:. We tried to use disk administrator to change c to another letter and then change e to c, but had no success. Any suggestions would be greatly appreciated.