I think you have to have pairs to support dual channel. Like 2 1gb sticks for 2gb and 2 2gb sticks for 4 gb... or dual dual channel using 4 1gb sticks.
I think its as long as two of them are the same/pairs
Like this......
Right now I have four slots, lets call it Slots 1, 2, 3, & 4.
Both my G.Skill 1GB RAM are on Slot 1 and Slot 3
Both are the same so I can run dual channel on it. So Slot 2 and Slot 4 are empty.
But if I decide to add more ram onto my system and take advantage of the Dual Channel on all four them, I dont think I necessarily have to have the same ram for all four slots. So I can have.....
Slot 1: G.Skill HZ 1GB 4-4-4-12
Slot 2: G.Skill 2GB 5-5-5-15
Slot 3: G.Skill HZ 1GB 4-4-4-12
Slot 4: G.Skill 2GB 5-5-5-15
But my RAM will be running at the slowest speeds, since all four of them are PC2-6400, they will be running at 6.4Gb/s at stock but timing will be 5-5-5-15 if not overclocked.
Even though I can run 1000MHz with a 5-5-5-15 on my HZ RAM, but say I cant run 1000MHz 5-5-5-15 on the new 2GB RAM, I wont be able to run them at 1000MHz 5-5-5-15. So if the 2GB RAM can run at 1000MHz with a timing of say 6-6-6-18, then thats the best thing I can get it at, is run all four of them at 1000MHz with timing 6-6-6-18. Or just run them at 800MHz with a 5-5-5-12 timing, if possible 4-4-4-12 depending on the 2GB RAM.