hdiutil is a Mac OS/X utility. It *may* be included with Darwin BSD for PC's, but IIRC, Apple has stopped developping and supporting Darwin.
.dmg is basically an ISO that's been compressed. A quick stopover at Google revealed this website:
http://vu1tur.eu.org/tools/
There, you can download a perl script that claims to convert dmg files to iso. There's also a windows binary version of the script.