I got 2 sticks of kingston 1gb and 2 sticks of patriot 2gb for my old PC. After all thing that i tried i got 6 gb total but 4 gb usable.
the sticks are put in 1gb-2gb-1gb-2gb sequence
Mismatched RAM usually won't work together in dual channel mode. Additionally, 4Gb is the maximum RAM usable if you are running a 32-bit OS rather than a 64-bit OS.