Bottomline: There is absolutely no difference between the dvds packaged in any of the versions ($29 "upgrade", $49 upgrade family pack, or the full retail versions) at the moment. This could change . . . At some point they'll start selling 10.6.1 or 10.6.2 disks and "may" change the rules. Making all the disks the same made producing the massive volume for launch day a lot easier . . .
Anyway, its up to you to decide which version to buy. You're already violating the EULA by installing on non-apple hardware.