To answer your question:
That build could be better equipped.
First off, Windows 7 Home Premium maxes out at 16GB of RAM. This means that if you want to put in 24GB total anytime in the near future, Windows 7 Home Premium will make only the first 16GB available for programs. You will need Windows 7 Pro or Ultimate in order to use more than 16GB of RAM.
Second, Premiere Pro CS5.5 needs more than 12GB to run at its best. However, since that build fills up all six DIMM slots to attain 12GB, you would have to discard some of the DIMMs in order to add more RAM at all. As a result, if you must have only 12GB, I'd recommend three 4GB DIMMs instead of six 2GB DIMMs. These days, 4GB DIMMs sell for about $40 to $50 USD each ($120 to $150 for 12GB, or $240 to $300 for 24GB) whereas a year ago they sold for $200 to $300 USD apiece ($600 to $900 for 12GB; or well over $1,000 for 24GB).
Third, Adobe does not currently support the use of any ATi or AMD GPU in its MPE GPU acceleration feature. This means that any ATi or AMD GPU, including the top-of-the-line models, will force MPE to run in software-only mode. And software-only mode is often 10 times or more slower than MPE GPU mode. At present the MPE GPU mode supports only Nvidia GPU-equipped cards with 896MB or more RAM and CUDA support.
Fourth, that HD 5970 is a dual-GPU card. Unfortunately, Adobe does not support the use of more than one GPU at all, which means that the HD 5970 goes half-unused in any flavor of CS5.x - and then, it goes to software-only mode, to boot since it's not an Nvidia GPU. As a result, the HD 5970 performs no better than an HD 5850 in CS5.x, especially since the HD 5970 actually consists of two HD 5850's on a single card. In other words, dual-GPU cards are a total waste of money, as far as Premiere Pro and After Effects are concerned.
Finally, if that system has only one hard drive, I'd strongly recommend adding two or more additional hard drives. This is because Adobe requires a minimum of two hard drives (one for the OS and programs, the second for everything else) just to run without severe slowdowns in performance. The more (hard drives), the better.
Randall that was an excellent critic for this thread, I would like to add one other comment. The i7-930 is coming to end of life. (Newegg is out of stock) I would suggest going with an i7-960 probably for no additional cost.
Thank you for the detailed answer. You bring up some additional concerns I now have about video cards and storage.
What video card would you recommend?
For disk drives, Adobe recommends RAID 0, and you mention even and odd number of drives.It is my understanding RAID 0 needs to have pairs of matched drives to work, correct? I am assuming, for projects, I want to have pairs of matched drives that are 7200 rpm, >= 1Tb, and good seak time, correct? Can a non-RAIID drive be used at the same time for the OS and other software?
Press the Overview tab at the top of this forum and read articles like 'To raid...', 'Generic Guide...' etc and you will find many answers to your questions.
For the video card, get a GeForce GTX 560 or GeForce GTX 560 Ti. (And edit the cuda_supported_cards.txt file to add the "GeForce GTX 560" or "GeForce GTX 560 Ti" or "GeForce GTX 560 series", depending on the name of the card that shows up in the GPUSniffer program that you run to determine the GPU, to the list.) Or, if you must have a card that's officially supported in CS5.5's GPU accelerated mode, get a GeForce GTX 570. The GeForce GTX 580, while very fast, is not worth the extra $150 USD over the GTX 570. And again, don't get a GeForce GTX 590 since it's a dual-GPU card with each GPU being slower than a GeForce GTX 570 (plus, since CS5.5 still does not support more than a single GPU, the GeForce GTX 590 will perform no faster than a GeForce GTX 560 Ti). ATi or AMD based cards are out of consideration because Adobe still does not support OpenCL GPU acceleration at this time.
And for RAID 0, you need at least two matched drives per array (it can be any number of matched disks as long as there are at least two of them). And you can have a non-RAID OS drive running with the RAID 0'd drives.