I'm starting in the fall, too. I live on the NW side of the city already, and don't plan on moving, but I also don't mind an hour commute on the train. As long as you live on the purple/red line, though, you'll have a pretty short commute. There's a number of great neighborhoods along those train lines. You can pretty much start your apartment search as early or late as you'd like--apartments are always popping up in different neighborhoods, all with different timelines for leases to start. Craigslist is a great way to find apartments and get an idea of price ranges, and can be great for finding roommates as well. (I've found totally normal roommates in Chicago this way, I swear.) There are also a number of free apartment search services. My last few apartments, though, I've just found by walking around the neighborhood I want to move to and looking for "For Rent" signs.
Here are a few guides to the city you might want to check out:
http://www.windycitizen.com/ clearinghouse of Chicago blog posts
http://www.chicagoreader.com/ the weekly independent newspaper
http://www1.chicagor...ies/chicago101/ the Reader's intro to the city from 2006--most is still relevant
http://www.yelp.com/chicago if you look around a bit, people post on almost everything