You shouldn't have too much trouble with your machine the way it is. it is getting a little outdated but Daz & Bryce should run fine, Blender should be smooth too. I would probably go with a new machine, rather then try to upgrade the video card. the speed jump to a G5 is pretty substantial.
Do you have classic OS9 installed on your machine? If you do, you can download Amapi 6.1 from this forum. It's a good modeler for precision stuff.
http://forums.polyloop.net/software-...html#post96903
here is Bryce
http://www.download.com/Bryce/3000-2...ml?tag=lst-0-1