Tom Baldwin wrote:
[...]

I'm having trouble getting Google to identify maufacturers of systems
with 939 socket (I don't want to get into the DIY game!). Can you
please point me at such manufacturers?

I guess that you'll have to ask them! You can also check out the motherboard (mainboard) specs on the manufacturer's website as a double check.

I assume they're faster than
Pentium D, yes?

That depends... :)

Check out TomsHardware for the latest comparisons.

In general at the moment, the AMDs run cooler and give better performance per buck than the present Intel offerings.

AMD have also had their designs ready for multiple-core operation a lot longer than Intel.

Good luck,
Martin