|The freeware Easeus Partition Master Home Edition is pretty good|
but it can't change drive letters already assigned by an operating system to a partition, at least not the one Windows was installed on.
You are allowed to make up to 4 Primary partitions on one physical hard drive, or up to three Primary partitions and one Extended partition that can have as many Logical partitions within it as you like, depending on how may driver letters are left that are available between and including C and Z.
E.g. Three Primary partitions could be assigned C, D, E by the operating system , the Extended partition could be assigned F, G, and H by the operating system for three Logical partitions made within it.
Or if you had three Primary partitions, and an Extended partition that has two Logical partitions and un-allocated space for a third one, if an operating system had already assigned C, D, E, F,and G, XP's Setup would use H for the drive letter of a new Logical partition made in the unallocated space.
What did you do the Backup with ?
It MAY be possible to change the drive letter it expects to be installed on to a different one.