You still need to find a Mac, but it doesn't have to meet the minimum specs for Marathon. Here's as good a place as any to start:
http://www.google.com/search?q="basilisk+ii"+site:lowendmac.com
: ...So I bought the Mac Action Sack, so I'd own nice legal copies of all the
: Marathon games. (And, incidentally, those other games too.) There is,
: however, just one problem.
: I don't own a Mac.
: *ahem* Is there any utility that will let me take the files from this CD, put
: them into Aleph One (or even emulate a Mac so I can play them natively) or
: is there another solution?