|You got it above. Any operation that is memory intense. |
I did a quick review of this thread and don't see your specs. In some cases there is no benefit to dual channel because the processor speed can't outrun the RAM. That is an oversimplification but makes the point.
You are over thinking things. If your performance is noticably slower then buy a dual channel kit. If your board can handle it you could get a kit with 2-2GB sticks. If your board can't handle more than 1GB per slot then you could get either a 2x512MB kit or a 2x1GB kit.
All 32 bit OSes can only handle 4GB of RAM and due to OS overhead you will only see maybe 3.5GB usable, even less if you have on board graphics using some system memory. So 3GB is a good compromise unless the cost difference is nominal.
One thing I didn't mention before. JEDEC standards for DDR2 is 1.8V. However, many makers juice thier RAM and use higher voltages. You MUST use RAM with the same voltage requirement in all slots. You can get by raising it on the lower one by .5V.
If SIW isn't showing the RAM voltage then look at the sticks or look in the BIOS to see what you now have.