Tough question. People will tell you that you have to have exactly the same sticks to make it work on the other hand I mixed different sticks and it also worked. You will just have to try.
In my opinion dual channel is just a marketing name it doesnt double your performance. I can tell you wont see any performance difference in games it's usualy around 5% even less.
Look for benchmarks using google.
Most benchmarks I have seen were using an athlon I dont know about intel but I think it should be the same, even less different.
Compare benchmarks using a 754 socket athlon with an 939 and you will see.

Dual channel menory got its start back when there usually were only two slots for ram. Running a matched pair increased the bandwidth from two 64-bit data channels to a 128 bit bandwidth with a dual channel enabled memory controler. It isn't required that identical ram sticks be used, but its recommended for best speed and stability. Using unequal ram sticks will cause the ram to run equal to ram stick with the slowest speed. A more complete explanation is available from Kingston Technologies.

One hazard in running unequal ram sticks is that they may cause the computer to crash out while in operation or simply not start properly. Its also best to check with the motherboard company to make sure what you're attempting can be done on that particular motherboard. If you already have the memory, you can try it and see what happens. If it works, then good. If it doesn't, just pull out the offending sticks.

Open Task Manager - Performance Tab. Keep an eye on Max Commit Charge, bottom left. If it never goes above 2048000, you do not need more than 2Gb!

Mike.

Since you mention that you can use all the memory that you can get, and would use 4 gig if it were possible, then I would recommend either using a 4x1 or a 2x2 ram setup. Windows XP will recognize about 4 gig total memory, but the amount available for use is less primary because of how much is used by the video card. If you have 4 gig of ram, then only 3-3.5 gig will be recognized for use, but it will run in full dual channel for best performance, though some will not be used. Further, if Adobe does release a 64 bit version, then you'll be set for that if you have a 64 bit operating system.

Other than that, if you don't want to spend the money for the 4 gig of ram or the task manager reading says you aren't using more than 2 gig of ram, then MrsBytch's suggestion of just running a 2x1 gig set of ram is good.