It depends. I always try to go for a motherboard with 4 RAM slots (as opposed to 2), & get my RAM in pairs for dual-channel functionality.
So 2x 1Gb would be better than 1x 2Gb. BUT if the motherboard you're getting only has 2 slots, then the latter may be desirable, even if you lose out a little on dual-channel.
Of course, if you get a 4-slot motherboard then you can opt for 2x 1Gb.
The E8400 won't be affected either way. G