I am thinking about starting to commute to college by a road bike. My commute is 30 mile round trip. I found a couple of bikes on craiglist, but since I am not an expert, I need some advice on which one to choose.

The bikes are :
2007 Trek 1000 road bike
Trek 1000 road bike
Trek alpha 1.1 road bike
http://houston.craigslist.org/bik/4417901637.html
TREK ALPHA 1.2 road bike w/shimano & bontrager
2011 Trek 1.2 58CM

I was looking to spend up to $450, but I am willing to spend $200 more. I will attach a rack to it to put my backpack on. I am 5'10'' and I live in Houston, so my ride will be on a flat area.

Thanks for your help.