Premiere Elements handles AVCHD video very well -- assuming you've got a somewhat powerful computer (ideally a quad core or i7 processor).
However, many of the Panasonics shoot 60p video, which the program does not work with well. I believe the TM900 has the option to also shoot in 60i. If it does, be sure to shoot 60i mode if you plan to edit your video in Premiere Elements.
If the camcorder only shoots in 60p, I would not recommend it for editing with other than a professional editing program.