They may run in dual channel.
You need 2 sticks of the same size and speed ie your 2 sticks of 512mb pc3200. They don't have to be from the manufacturer but they need to be similar in timings for complete stabilty.
This is why it is better to get 2 sticks of identical RAM but not essential!
I'm betting your RAM will run in dual channel mode
BUT ONLY on certain Intel motherboards and AMD socket 939 boards so if you have a socket A board (and XP CPU) or socket 754 you won't be able to run it anyway as dual channel is controlled by the Athlon 939 CPU.
Basically it's a faster way to read/write to RAM and will see you maybe a 5-10% boost in gaming for example.