Well our Cores are typically i945 motherboards with 3.0Ghz Celeron's and 512mb of RAM and ours are configures as hybrids so they also perform as MD's too. Our Hybrid cores can reliably support 3-4 pxe booted MD's in this config. That at least gives you some metrics to base a decision on.
Hope this helps
That actually gives me a pretty good idea.. I'm sure that a 4x900mhz p3 with loads of ram can probably handle the load of at least 3-4 pxe boots. regardless, it's not like i couldn't find a use for a machine like that if it didn't work.
Now, I guess the only question left is how important are the specs for the MD?.. or can they be basically barebones aside from the sound and video cards?