I've written an FPK packer for Tatsunoko vs Capcom. It will scan a folder recursively and compress the files into a fpk. The fpk files generated by the packer can be unpacked with unFPK, but I haven't been able to test by replacing files on the ISO. The files are generally larger by around 1k or 2k than the original fpk files. The entire file format is accounted for except for the first 4 bytes, which changes from file to file. I think it's a checksum, but I haven't yet been able to figure out how it's computed. Hopefully TvC will accept FPKs with the first 4 bytes set to zero. You can download the tool (and VS2005 source code) here. CODETo create an FPK: fpktool -p To unpack an FPK: fpktool -u Would anyone like to help with testing?