Upgrading from 2GB to 4GB of RAM

[amberland]

My computer has 2GB of RAM (two sticks of 1GB). I'd like to upgrade to 4GB in hopes that it will get rid of my persistent Error Code 12 problem. I figured I'd buy two sticks of 1GB, but then I read this:

However, because of the need to install in sets of two or three, we recommend the following:

2x1GB (total of 2GB) of DDR2 RAM ... for Windows XP

2x2GB (total of 2GB) of DDR2 RAM ... for Vista and Windows 7

Purchasing this way also uses the least amount of RAM slots. Some motherboards become temperamental when all RAM slots are filled.
Question 1: If I have Windows XP, can I upgrade to 4GB of RAM? Having two sticks of 2GB is only mentioned for Vista and Windows 7.

Question 2: Is there a way to find out if my motherboard will become temperamental if I have a total of 4 sticks of 1GB? Since buying two sticks of 1GB would be cheaper than completely replacing my current RAM.

[Whiterudder]

You can upgrade to 4GB under XP, but the full 4GB won't be used - most likely, around 3-3.5GB will be used. This is not the case if you have Windows XP 64-bit, which is quite rare.

No. All motherboards should work fine with all RAM slots filled, and mostly they do. But sometimes they don't - it's just one of those things. I'm afraid you have to stick a hatpin in it.

[amberland]

One more technical question (I'd ask the people at BestBuy, but they usually seem to know even less about computers than I do)

The invoice for my current computer says:
Memory ( 2048MB [1024MB X2] DDR2-800 PC6400 Memory Module Corsair-Value or Major Brand )


So I'm guessing the new memory should have the same specs? It should be DDR2, have the speed of 800 MHz, and be the type PC-6400?

Is PC2-6400 the same as PC-6400?

[edit: From my research I found out that PC2 and PC is the same and what's important for my motherboard is that the memory is "DDR2 800/667/533". Preferably 800, since that's what I already have and anything else would slow things down.]