Create hard links on CDs

[Rober2D2]

I have seen several CDs which have about 1 GB data. They are not HD-burn CDs (I am sure because my drive cant't read them). What I think is that there are "hard links" inside the CD filesystem, so that duplicated files have more than one directory entry, but data is written only once (more than a directory entry per file). An example is a W2k that has the three distributions (pro, server, adv. server), where many files are common to the three distributions, but are on different directories. I don't want to copy that CD which is quite easy, but to be able to do a similar thing. I know how to create hard links on hard drive, but not on a CD or ISO image.

Does anybody know how to do that?