i think the easiest way is to get the memory you think will work, obviously save everything about the RAM you buy and buy the same in the future, or you could try this although it couldn’t identify my current RAM but it may work for you.
For that motherboard and CPU, you’ll need DDR400 (PC3200) RAM, non-ECC. ECC is error checking system and is only needed on critical servers. The PC3200 defines the speed at which the RAM operates at.
well basically if the RAM has chips on only 1 side - its low density, high density RAM has chips on both sides of the DIMM
usually only systems over a maximum instalable of 1.2 Gig RAM will take high density RAM
yeah, should be ok, i think generally low density RAM is ok for most people, i think high density RAM is more for people who want the best of the best, not sure if low & high can be mixed in the same pc (i could be very easily wrong about this, please correct me if i am)