"Special" iso files

[PeakDX]

Hi
A while ago i saw an iso file which when mounted had 1800mb, the iso file itself was around 650mb, it had 3 different directories that had the same files but with different aragement and different filenames... now i am looking for a tool to create something like that... or a link to a iso file specification so i can try to make it myself :-)

tnx

[NARS]

I think that UltraISO is capable to do this.