To be honest, I never used this compression that comes with NTFS (WiNNT and derivates support it). What I do know from compressed volumes, is that I never ran into a system that supported the uncompressing of a volume, without loosing data.
If there's no data on the disk, there should be no problem turning the compressed drive into a regular disc. Merging shouldn't be too much of a problem either, but I don't know a (free) MS-based solution.
If you are comfortable with Linux, you could download Knoppix (full Linux distro on a CD, boots from CD, www.knoppix.org) and do the operations with some Linux tools. If you want to know more about this, I (perhaps) can help you. Just be aware, this is pretty risky and rather complicated!