On a mission with a vision - but when do I start?

I have a mere 20 weeks left of college before I graduate from the University of Wisconsin Oshkosh in May 2010. I'm excited. I'm nervous. I'm curious.

Many people (i.e. Career Services, friends, professors) have suggested to start hunting for jobs early. I am more than willing to start a search for my first job out of college, but it seems too early to start applying for jobs.

If a business has a job posting on their site or another recruiting site, I assume they are looking to fill that position within the at least the next month of the original posting. If they aren't planning to hire that early, they will probably at least review applications and start to interview people within a month or two.

My point is, I am not technically available to start a full-time position until May 17, 2010. Therefore if I apply for a job now, what employer is going to wait for me to graduate five months later?

At five months from graduation, what kind of things should I being doing to "look" for jobs or put myself in a position for a job after graduation?

How far out from graduation should I actively pursue jobs (fill out applications, send cover letters, inquire about job openings, etc.)?