There's no such thing as dual channel memory,if the two sticks you've got now are exactly the same,then you can probably run them in dual channel.It depends on which slots you use,it's either 1&2 or 1&3.Check your manual to see,or post your motherboard make and model.Also,is there any reason why you want 4gb of memory.
WHAT'S YOUR motherboard/chipset? amd socket 939 and intel's cpu runs dual channel. If you have socket 754, then you would be running at single channel only. You can't run dual and single together, the system would either run at dual channel or single channel alone.
Peterdiva is absolutely right. Memory marketed as "Dual Channel" is just a set of two of the same DIMMs. If the memory you have is the exact same model than you can probably run in dual channel mode.
Depending on your mother board there are a few ways to do this. Either by selecting dual channel in the BIOS. Or if you don't have this option in your BIOS (this is the more likely senario) you probably have four DIMM slots on your mother board. If you populate slots 1 & 3 or 1 & 2 then you will get dual channel. This is the most common layout.