i believe i have seen an 8gig stick but a single 32 bit cpu can only address 4 gigs most usere will not need over a gig as of now unless you are heavy into graphics
ECC is slower and for home users not better but it is important for things like servers (which require it) where an erroris a huge problem
for the fastest i think they have like 550 mhz ddr now but IMO its best to runn it at the same speed as your fsb
practically any reliable brand that is pc3200 should be great with any cpu ATM but it might do you well to get some pc 4000 or so if you plan on oc ing a 200fsb cpu also if you get ram with cs2 it will be faster and if you arn't ocing the ram you wont need to loosen it
Why is DDR a better option than RD-RAM? Or is it not? I say this because it seems as if the market is going away from the RD-RAM chips b/c more and more out now and coming out (even gaming mobos) motherboards have DDR capibilities, not RD-RAM.