Heh, someone post that link to the 5.45x39 hunting pic :) If my wife wernt the family designated hunter now, I might test the sub-cal hunting ability.
To get down to it, I'd probably avoid an assault rifle on the hunt and take one of my Mausers or an Enfield. For one you can hunt anywhere in the US that allows rifles with them, and quite a few foreign countries too. I took one of my .303s to Mexico a few years back for hunting with very limited problems.
For another, if you're a new hunter, I guarentee that you'll end up running all over tarnation trying to track down the mulie or white-tail you tagged with a .223 but failed to hit accuratly enough to guarentee a disabeling shot.
Finaly, you can get a C&R mauser or even a Mosin Nagant and stick it in a sporterized stock and saddle it with a wide range of optics and mounts for less than you can buy a stock for an AR type sometimes. If you go with a Mauser you can grab ammo for dirt cheap for target practice, and hunting ammo is universaly avaliable.
Having some board drill Sgt.s and rangemasters willing to look the other way, we were often encouraged to "plink" the deer that overrun most ranges at Ft.Knox this last February. I will attest to the fact that a .223 will pretty efficiently kill a dear if you get it somewhere vital.
Not telling you to go for an AR, I got my first real rifle when I was 14, it was a Norinco SKS. I bought it for the exact same reason you're looking for your AR. I never ever even took it into the woods. That was, eleven years ago now, and I've gone through an amazing and bewildering array of firearms, well over 200, and I never realy spent any money on it. $95 here, $200 if I got lucky there, I paid for all my weapons and learned the art of bickering over prices at gunshows. I traded my entire collection about every four months and while I had a lot of nice toys pass through my closet, I learned a lot more by trading off every so often.
My final advice for you is, if you can afford it, get your AR now for fun, and spend an extra $100 on an old Mauser or something for hunting. It'll serve you a lot better in the end that way.
Ultimatly firearms have played a larger role in my life than graduating college, going into the Army (so far) or getting married (again, so far). So welcome to the addiction and enjoy yourself, just remember to be safe