will any DDR ram work? they have DDR-SODIMM, DDR2, DDR2-SODIMM etc. does any of that matter?
Not just anything will work. You want 184 pin DDR400, sometimes called DDR PC3200. Timings of 3-3-3-8 or lower would be good.
Here is an example: http://www.newegg.com/Product/Product.aspx?Item=N82E168...
You will also want to by an identical pair of dimm sticks. This way you can take advantage of dual channel operation. Notice that my example is an identical pair of dimms?
Oops. I forgot to mention something. The ram you listed is Registered, ECC memory. It is used for servers. You want non-registered, unbuffered non-ECC memory. What you need really is the most common type. The crucial ram you listed actually has a 9th chip used for parity checking. It's useful for servers but actually runs slower than standard ram.
Try this from Crucial (Micron): http://www.crucial.com/store/mpartspecs.aspx?mtbpoid=52...
Socket 939 motherboards usually support up to 4GB of ram, using all 4 slots.
Check the specs on the motherboard you want to buy.
However, unless you will be using a 64bit operating system, you will only need 2GB. A 32 bit OS can only address 4GB max, and in practice will only acknowledge 3-3.5GB. In addition, if you open up Windows task manager and look at the performance tab, you will see your peak commit charge is less than 2GB. It's probably less than 1GB. Your total (the current usage) is likely to be 250-300MB or so, since you are surfing the web. As you can see, 2GB will be plenty.
64 bit is not compatible with really anything at the moment go with the 32 bit this way you ont have problems
Where do you get this from? That is as far from the truth as possible. I have run x64 versions of Windows, including Vista 64, since they came to light and have had very few problems, I run all apps I need without problems. And I know that lots of people do the same...
To answer Travass185's question: If you buy Vista Ultimate, both the 32 and 64 bit versions are included.
If you get Vista Home only the 32 bit is included but with an option to pay a small s&h fee to receive the 64 bit by mail.