I know the sticks you're thinking of, and I have to agree; Kingston used to use the "Two on this side one on the other" arraingement a while ago. If it's a solid bank on one side, it's single bank, if it's split on both sides, it's single bank, and if it's solid on both sides, it's two banks, right? Some P4 chipsets to this day won't allow double bank RAM stick in the last RAM slot, so it's a valid point. And I think he was talking about using PC3200 (DDR400) in a PC2100 and PC1600 only motherboard, just got a bit confused over some specs. Double and Single bank DIMMS have no bearing on memory speed ratings, so stick with PC2100 DIMMS as they're cheaper.
What kind of motherboard is that, anyway, since it might be capable of faster RAM speeds then the advertised DDR266?