What kind of memory do I have? What should I upgrade to?

Hi, I have built a new system and bought the RAM from an online WEB store, because I had store credit from a previous transaction.

The RAM works fine, but I am not sure what brand it is or what the specs are. The Web store "thinks' It's Infineon. It has no brand name, but has a LOGO that looks like a pyramid or delta with horizontal stripes.

It is described as 1.0GB PC2-5300 (667Mhz) 240 pin DDR2 DIMM.

(had to set the bios to provide 1.9 volts... unstable until I did that)

I bought 2 to use dual channel.

I have an ASUS M2NPV-VM mother board, an AMD Athlon 64 3800+ processor. I have my current ram installed on A1 and B1 to provide dual channel.

I would like to add 2 more GB of Ram to slots A2 and B2 to give me 4 GB. So here are my questions...

what is the difference between PC2-5300 and PC2-5400? Are they compatible?

Since I am adding a second dual channel configuration, does it matter what the first is? Will one affect the other?

While I would like to get the best performance, I do not want to pay more if the speed and performance is going to be dictated by the lesser brand of memory specs.

I am not particualarly interested in overclocking, although I may try at some point. This was built to be a home theater PC so running cool and quiet is more important.

Any advice is greatly appreciated.

Phil