Yes, like a computer does not need a gfx card technically.
However, the major advantage to socket 939 over AMD's old and discarded socket 940 is registered memory. Registered memory boosts performence by quite a bit and is NOT only for opterons and other server class CPU's.
However, considering your budget. It might be wiser to upgrade to this later.
registered memory is a little slower actually, but the small chip that is added to the memory module can address twice the amount (so no more 512MB/Module max, but 1 GB/Module and more)
Your old memory sticks won't work on the new one...
My checklist for this kind of project is:
- Get a reasonable CPU (mid-range Athlon 64, or the fastest Sempron, which is a 32bit limited Athlon 64)
- Check if your current PSU does at least 300W. Replace it when it gives less
- Get a Motherboard from a make that has been around for a while. IMO MSI is OK for normal - medium use, but go for Asus or other medium/high priced ones if you plan to go to the limits.
- Chipset: nForce is one of the fastest available for AMD
Master-slave is easy (don't believe it if someone says it's difficult)
Each cable can only have two devices one is master, the other is slave. If you have one device on a cable it should be master