How much memory do you have? which iMac? running any other apps?
If it's a regular Bondi Mac that came with Nanosaur, I don't know why it should be wussing out due to memory... Apple designed Nanosaur/Bugdom to be demo apps and run on basic configs, so they shouldn't be demanding. (yeah, I know, should-could-would...)
Are there any other apps running? Running recently and maybe still hogging RAM? hard drive space/cache?
otherwise... ?