I have withstood the temptation to upgrade to -current for the past
months because radeonfb didn't recognize my unorthodox monitor
resolution by default.  Instead I got the same result as described in
http://mail-index.netbsd.org/port-macppc/2006/11/10/0006.html.
(Coincedentally, my card is also an ATI Radeon 9200)
After deciding to tweak the modelines file, I got radeonfb to run with
the folowing modeline:
ModeLine "1280x768"    105.64  1280  1312  1712  1744    768  782  792
 807 -hsync +vsync
It works, however there is a brief moment at the beginning of boot
when the screen goes black.

My question is: If working modelines are reported, will they be
commited into the file sys/dev/videomode/modelines?  I would like to
be able to boot off future install CD's without any tweaking.