As i said and winny said, CASE UPGRADE NOW!! COOLING NOW!!thennnn everything else should wait to come in one shot
4. The matrox cards are great however, as crix said alot of those cards are soft/hard modded derivatives of the desktop part kin. (Note crixx there are differences in the higher end range). I would suggest unless he is getting a matrox for some proprietary encoding tech, sticking with a desktop card is fine and will be cheaper. Also recall that Avivo and Purevideo are features of existing ATI/Nvidia desktop and workstation cards. Thus encoding on the video card (which albeit in the infant stages) will provide better results in the long run. At which point the CPU encoding of video will take a back seat.
wait till october or november for some mature ish conroe platforms and sweeter conroe pricing, ddr2 pricing should drop a bit more as well.
7. If you are going with the 939 vs. the AM2 socket, can I suggest DFI or Abit as alternatives to Asus/MSI/Biostar. It will cost you more to get teh DFI or Abit but for feature set and stability the others can't come round. I would also suggest looking into the Crossfire platform as it's a better performer (Crossfire 3200) than the Nvidia nForce 4 chipset.
Iunmached ram isnt a problem. As long as each module is running in spec it's fine.
DO realize that the cheapest thing he can do for a boost in video processing, is buying a dual core socket 939 cpu. no it's not AS fast as core 2 duo, but given that he's already running 939, it's the highest bang per bug for him. ESPECIALLY with ddr2 prices at a rediculous high. Oc'd to 2.7GHz (the average) he's have something compeditive to a e6400. (yes i DO realize core 2's oc well over 3.0GHz)