I'm familiar with Voodoo, they've been around for years, along with Falcon, Alienware, etc. Good stuff, WAY overpriced.
This particular system used a dual Opteron board, which is the only way to get the extremely high ram counts. It supports up to 24GB (Voodoo only sells to
, however not at full speed. That type of configuration is only meant for servers, where memory bandwidth is not as critical as memory size (mainly SQL Database servers).
The board Voodoo happens to be using for this system is the Tyan K8WE. The large price jump from 4 to 8 that you see is due to 2 factors. First, there are 6 ram slots on the board. In order to use the 2nd bank of ram (slots 5,6), a 2nd cpu has to be present - so you add another processor. 2nd, with only 6 slots that means you need to use at least one 2GB stick - which are MUCH more than 1GB sticks due to no demand and low production.
The board technically supports up to a 4GB stick x 6 slot configuration, however the cost would be well over $10,000 in ram alone. It also requires at least one registered stick (more expensive) and you want to match the setup, so that really means 2. That is a drawback of the Opteron chips right now as opposed to normal Athlon chips, that do not require registered sticks (cheaper).
When all is said and done, Windows XP and Photoshop will not show you any benefit above 4GB. Windows does not use more than a few hundred MB to run, and as you know PS can only use 3. To utilize such a setup as this you need Linux, WinXP64, Win2k Advanced Server (or XP Server), and apps that can use the full amount (such as SQL Server).