First, this is what I use now:
CORE2 QUAD Q9450
3 GB DDR3
GEFORCE 9600GT 1GB
GEFORCE 8600GT 512MB
1 500GB SATA SYS DRIVE
2 1TB SATA MEDIA DRIVES
750W POWER SUPPLY
WINXP 32

3 MONITORS (left for media bins, center for timeline/editing, right for full screen previewing)

Now I'm thinking of going to Win7 64 to take advantage of CS5 Production Prem. I don't want to do a complete rebuild- so I am going to make some minor upgrades to take advante of a 64bit OS and NLE.

I am going to keep the CPU, but bring the ram up to 8GB DDR3 and add a GTX 460 video card for the CUDA needs of the Mercury Engine.

Currently I use these three monitors to work. The center and right screen are run by the 9600GT (editing/previewing), and the left screen is run by the 8600GT (media bins). Since I can't find an affordable Adobe CS5 certified GPU that supports more than 2 monitors- I have to use two video cards. I want to do this instead:

Pull the 8600GT and toss it on ebay. But I will continue to have 2 GPUs in the new machine: A GTX 460 to run the center and right screen, and the 9600GT to run the left screen for the media bins.

OK, so on to the real question. As my PC stands now, I only need one driver to run these 2 Geforce cards. If I do what I am proposing- I will need a driver for the current 9600GT and one for the new GTX460 in Win 7. Will this work? And if so- what will Premiere choose as the GPU to run Mercury through? I want it to use the GTX as the main GPU for editing and monitoring, and the 9600 as an extra screen for bins only.

Do GPUs work like ram, where your graphics will only run as fast as the slowest card installed? Sure, the easiest fix is to have 2 identical GTX cards in the machine- but for cost, power req, space, and heat issues I don't want to have to buy 2 GTX cards.

thanks

I have a GTX 260 and a 9800GT in my PC (Core i7 920 based machine, highly recommended as its cheap and fast). I don't believe you mentioned this, but there is a "hack" to use unsupported Nvidia GPUs for the mercury playback engine (MPE) in Premiere Pro. It's not really a hack, it just involves editing a text file and a video driver configuration setting. Here's a great link on the list of your cards, including your 9600GT and 8600GT.

Adobe Premiere CS5 Video Cards with CUDA Acceleration Mercury Playback Hack Mod Tip Unlock (http://www.studio1productions.com/Articles/PremiereCS5.htm)

My GTX 260 is in the first PCIe x16 slot of my motherboard, so apparently the PC sees it as the first video card in the Windows 7. So assuming you leave Premiere Pro in one of the 3 monitors that is connected to your 9600GT, you should get MPE hardware acceleration. Besides the power of the GPU, you'll need a minimum of about 800MB of ram on the video card for this to function.

If you get the GTX 460, I haven't read the updated forum pages at Adobe Forums or here at DVInfo, but there's no reason why the GTX 460 wouldn't work as a "hacked" video card for MPE. I was try to leave most Premiere Pro windows in the GTX 460. It's unlikely there will be a negative impact if the 9600GT monitors have the bins and some windows in them, but if you can keep them on the 460, that would make sense.

Look here to see the 460 results: PPBM5 Benchmark (http://ppbm5.com/index.html)

I have just looked at the list. The rather long MPE times out of the GTX 460 came from slow systems (or those which have limited bandwidth potential on their memory controllers) - those equipped with pre-Nehalem Intel processors as well as the newer Lynnfield i7-8xx processors. And since the OP has only a Core 2 Quad, expect the results to be much closer to those of the slowpokes than to those of the three Bloomfield i7-9xx systems on the list that use the same GPU. And going to a GTX 470 or GTX 480 would not be worth it for such a slow system because the absolute timeline rendering speed would have been limited by the older CPU.

This is what you do: the GTX 460 must be the #1 & #2 displays within Windows and Premiere will see the 460 as the main Gfx card. Another member here, Tim Kolb, has a similar setup but he is using Quadros, FX4800 and FX560 and he has the FX4800 as the #1 & #2 displays and the 560 as 3 & 4.

However, I asked Tim to put the Program Window on the FX560 to see if hardware acceleration still worked, and he reported back that it worked just like it was on the FX4800; so, I think Adobe is able to route the video through the FX4800 first and then to the 560. I know this is sort of how it works with an Aja Kona, CS5 and MPE acceleration - the video is processed thru the FX4800 and then sent to the Kona. Tim has the Kona in his PC and I am just repeating what he has said in his Premiere Pro class at fxphd.com.