Could not find a Samsung stick, or any recognized brand with the right geometry, so i rolled the dice on a chinese ebay vendor offering "4GB 2Rx4 PC2-6400 DDR2 800Mhz 240Pin RAM Desktop Memory Only for AMD chips" -- it arrived about 10 days later and my imac g5 isight seems to be using it just fine.
I recall vaguely from 15+ years ago that in the late days of ddr2 before ddr3 took over completely, AMD systems could use high density dimms that intel systems could not. *shrug*.