Design software for Mac

I'm not sure this is the correct thread for this question, if it is not I do apologize to everyone.

Currently I am using Google Sketchup to design some buildings and other misc. things on my Mac Mini G4. I would use Blender instead, but I do not know how to use every tool in it to do simple stuff or complicated items.

Does anyone know of a not to expensive design software that could run on a Mac Mini G4 that does not cost a lot of money.

Here are the stats for my mac:
I am running 10.5.8 Leopard as well
Processor- 1.42GHz G4
1GB of ram.
with a 32mb ATI Radeon 9200(I know this is low, but I use Final Cut Express 4.0 on it and there is no issue of it crashing or any lag due to the low amount of video ram)


Thank you.