Thanks Elfen, olePigeon -- Turns out the SIMMS I had were composite--  I read somewhere that Apple did not recommend composite memory.

I sent them back and picked up some 4M, 9 chip SIMMS, so I should be able to get the SE/30 up to 32MB. I'll be running 7.1 for now, and I'm not sure if it's worth running 7.5.5 on it.  But 32MB should be plenty for a while. It's much better than the 2MB that's installed now..