Accomodation for Oktoberfest does book quick for sure. I would recommend one of two things:
1. book something asap online if you want to put your mind at ease knowing that you have a place booked for the festival. Take what you can get as you might not get ideal accomodations (ex. private room with a bath). The prices are higher during the festival. I just checked and found dorm beds available at the three hostels I looked at.

2. If your feeling friskey: plan to get to Munich very early in the morning and find accomodations when you get there either hostel or private. There are many locals who rent out their flats and apts. for the duration of the Festival to make a few extra bucks. When I went we ended up renting a shared flat with about 6 other people. This was not an ideal accomodation (8 beds in a one room flat), but it was reasonably priced and close to all of the action!

Book now.
Try Euro Youth Hostel and Wombats hostel (I have stayed at both while in Munich— not for the fest though).
When I went to the fest, I stayed at Hotel Jederman: minutes walk to the fest and the train station.
When I went for the fest, it was booked a YEAR in advance, the hostels have more restrictions that time of year…
But since MILLIONS of people attend the fest, it is safe to say, book NOW.

Have FUN, I am very jealous: best time ever!

Ok thanks heaps guys! Will get on and book some straight away!!