Comparing Dual Channel and Single Module Memory

I recently purchased a new computer to test and review video games and PC hardware. When purchasing the computer and after deciding on the company, CyberPower, the general type, AMD, and the type of dual video cards, Crossfire, I had to ask about memory. What type does the motherboard I am purchasing take and what should I get to tide me over until I receive some as part of testing and reviewing.

I found several articles about the different companies and their best performance memory modules but could not find an answer to a few more basic questions. Does it matter if I use two 512 megabyte memory modules in dual channel or should I get one 1 gigabyte module? Can I test this using current testing methods and have the results make sense?

When I purchased my computer the memory was a bit expensive so I decided to purchase some after I received my computer. I bought a Transcend 512 MB stick to tide me over until I found out some answers to the questions I was asking and not finding answers to.

Just what difference does one stick or module of memory compared to two modules in a dual channel motherboard make. Both the single module and the two modules need to be the same amount when considered in my test and they should be basically the same type so I set out on the first part of my mission, getting memory modules from a memory company. I contacted various memory module manufacturers and Crucial Technology was intrigued by my idea and sent me three memory modules, thank you Crucial Technology.

I knew I could test the modules using Futuremark's PCMark05 and also using some simple game testing. I contacted Futuremark and received their current benchmark test program PCMark05, thank you Futuremark.
I received one 1 gigabyte DDR2-800 PC6400 128Mx64 memory module, part no. CT12864AA80E and the two modules of 512MB are 2x 512 megabyte DDR2-800 PC6400 64MX64 memory modules, part no CT2KIT6464AA80E. For my tests I would also be testing the memory modules I had when I first received my computer and installed them. I had an Adata DDR2-800 PC6400 part no M2OAD6G3H3160I1E58 and a Transcend DDR2-800 PC6400 part no JM367Q643A-8.