1) Dual processors are labeled as SMP. SMP enable apps and games are nt 4, win2k, xp pro, quake 3, photoshop, maya, 3dsmax, etc. Check with the app or game to see if it is programmed for SMP.
2) The best values on this PC are the Case, Power Supply, 18GB drive and the 2 CPUs. The case isn't sold separately. The PSU is powerful and designed to power a ton of crap.
You could build a rival to this PC using AthlonMP dualies, but to get similar features you're probably going to exceed the $999 price. When building your own, you don't get the Compaq warranty. It's quite helpful on machines of this caliber.
1 2ghz P4 running photoshop is slower than 2 P3-933 running photoshop. In other words, if the software is coded to utilize SMP, then it will smoke the P4.
I checked out Tekbargains and they have a link to get a dual capable Poweredge server from dell for $661. While this is good, the dell comes with 1 processor and a 1 year warranty. I think this machine is highly worth it for those of you not into building your own computers.
Correct me if I am wrong, but I don't think Half Life or UT is coded for SMP. Therefore a server would only use 1 of the processors.