Personally I love running my scope cards in a 2nd system, but that's because I use it primarily for 2-3 signal paths at at given time (Solaris and/or a nice Modular patch and then a few effects chains).
The PCI bus is the MOST IMPORTANT ASPECT of the system, and second to that is the graphics card (high end 3d cards, especially ATI can swamp the system bus with their drivers which want the system entirely to themselves for high framerates in games). Just to give you an idea, I run Scope on a p3-700. That's an old Intel bx chipset (100mhz fsb even, slotket adaptor to get a 700mhz cpu into that box), 512 Mb ram and an old Matrox g400. Scope runs just fine although it does load new projects a tad slower than someone with a modern system.
Also, if you intend to use Scope in a standalone system you might want to consider wiring it to your main rig with ADAT as well as midi & analog i/o.
Looking at your motherboard (
http://www.amdboard.com/asus_a7v600.html ) the biggest issue you might face is the fact that it's a VIA based motherboard. In general you'll want to steer clear of VIA & Sis chipsets unless you don't mind doing a lot of hand tuning of your system. They have extremely poor PCI bus performance and you're likely to see a lot of PCI overflows. For AMD the positively ancient AMD760/761 and the nforce3 based motherboards tend to be the best. But since you already have that motherboard you should ask other users here how to optimize it as best as possible. Visit the tech section here on PlanetZ for more info. Just keep in mind if you experience headaches with that motherboard that it's not Scope's fault Any other dsp system (UAD, Powercore etc) faces the same limitations of the PCI bus.
As for your friend's headaches, I can only say that it's really not intended to be run in 'VST mode' (XTC mode in Scope terms). There are users who use it that way but the functionality was sort of 'tacked on' to meet the demands of users who were insistent that they had to have it once UAD & Powercore started shipping similar systems. So the code works but it will require workarounds on your part to get a lot of things working under XTC. There are people here who are perfectly happy running XTC/VST mode with their cards but the general consensus among most users is that the standalone OS mode (scope.exe) is far preferable for its flexibility.
As for other instabilities, most problems are related to inexpensive motherboards (crappy chipsets) or using a sytem with an Intel p4 & HT (hyperthreading). Some dual core users are reporting issues but it isn't clear currently what the problem is as others with nearly identical systems have no problems. All in all it basically takes a bit of tuning if you find you have issues then everything is smooth sailing. Give yourself a month or two to learn the ins & outs (so to speak) of the Scope routing and you'll find the system is really fairly easy.
