If you want your end product to be CD, for simplicity's sake you may want to skip going to a DAT and purchase a standalone CD burner.
Basically, you connect the stereo mix out of your 424 to whatever you want to mix down to (DAT, CD burner, computer, etc.), hit record on the device which holds the medium to which you are mixing, hit play on your 424, mix as necessary, then when you're finished, hit stop on both devices.
You will generally connect to the DAT or CD burner with RCA/phono cables. If you wanted to mix down to your computer, which would probably be your cheapest option at this point (as I assume you own a computer since you post on this forum, and this computer more than likely has a sound card), you can connect your 424 to the line-in of your soundcard. To do this, you'll need an adapter or cable that goes from RCA-1/8" stereo (like a standard headphone jack). You can get this for about $5-$10 at Wal-Mart or Radio Shack.
You will need some kind of software to record onto your computer. Some free programs include Reaper and N-Track. I realize this is the analog forum, but as you mentioned that you want to eventually release a CD, this is probably the cheapest way of getting there. Although you could look into purchasing a better sound card or a standalone CD recorder, I don't think that when recording from a 424 that you are going to lose a lot in terms of fidelity. This may not be the easiest option, but it doesn't take very long to figure out how to record 2 track stereo in either of those programs. The only thing you'll want to make sure is that when recording to digital (to get the CD) that you are watching your levels very closely, because if you clip (go over 0) it could sound really bad.
-MD