Fact: The i815 chipset, in any incarnation, on any mobo, only supports 512MB (max). Why 3 slots? You can fill it to capacity using a combination of 128MB and 256MB sticks (if you wanted to).
Fact: The CUSL2 is one of the very best mobos available today. One of my two (non-oc'd) systems has a CUSL2 and 1Gig P3. It's been running Win2K 10-hrs/day, 6-days/wk., ever since I put it together about 6 months ago without ANY problems whatsoever!