antohnee :
does it NEED to be dual channel?
No, but you will get better results if you have a matched pair of RAM to take advantage of dual channel.
Here's is an example of price differences that I've found on newegg.com:
DDR2 533mHz 2x1gig chips (dual channel set) cheapest that they have
$71 shipped
pqi POWER Series 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 533 (PC2 4200) Dual Channel Kit System Memory - Retail
http://www.newegg.com/Product/Product.asp?item=N82E16820141224
DDR2 800mHz 2x1gig chips (dual channel set) cheapest that they have
$80 shipped - $15 MIR = $65 shipped!!
A-DATA 2GB (2 x 1GB) 240-Pin DDR2 SDRAM DDR2 800 (PC2 6400) Dual Channel Kit Desktop Memory - Retail
http://www.newegg.com/Product/Product.asp?item=N82E16820211066
You decide which one is cheaper. I'd go with the DDR 800mHz A-Data ones, for the simple fact that they are faster and cheaper, but that is just me.
My 2cp's