You'll need a soundcard to go from DAT(I assume) to the computer.
Then you'll need software to record that file on the computer. If it's only from DAT, there are many programs out there that will do this job. (Scott, is Coaster available for OSX?) There's also Spark, Peak (though I don't like their software), and the like for cheap, and the big boys of Digital Performer, Logic, and Nuendo for major $$ but with very good editing capability.
I recommend Spark XL for what you're doing + Scott's xACT interface.