More discussions on chippers here:
http://www.orangetractortalks.com/forums/showthread.php?t=4442&highlight=fitchburg+chipper
Including my reasons for buying a self powered chipper over a PTO powered chipper.
I have to agree with Eric,Renting one might be economicaly more feasible than spending a $1000 or more to purchase one for your tractor to power.
If you decide to go the Tractor PTO powered route you have to decide which type you need, There are the basic gravity feed knife chippers and then there are the self feeding type, Do you need a chipper to chip trees or do you need it to chip up branches and brush.
Over the course of my life I have spent a lot of money buying things that I wanted only to find out they were not what I really needed, In most instances if I had taken the time to sit down and actually determine what I needed in a piece of equipment or vehicle I could have saved myself a lot of time and money, It has been fun though.