I am no expert, but this is just my opinion. I agree about the gpu. Don't totally skimp on it but you really don't have to put much emphasis on it either. Vegas pounds the CPU and memory. So I would agree with the i7. Even the entry level i7 is on par or slightly better than the extreme core2 quad. Besides the basic i7 can be OC'd into the mid 3's safely. Next I would say 64bit and load up on the RAM. Use a good name and as much of it as the budget allows. After that I would say plenty of storage.

Today I would blow up the RAM - maybe something about 12 GB or so? And take here quality as said before. Windows 7 will be fine as far as I hear - but be aware that up to now Windows 7 is not supported by Vegas.

My new Vegas PC has been rock solid. But I spent a lot more than $2K on it!

If I were trying to do it cheaper I'd do i7, 12GB RAM, 2 decent hard drives, NVidia graphics card, Windows 7.

1. I7 920 overclocked to 3.x
2. 12GB RAM - don't waste money on high speed ram - you won't see a difference in performance really - get some that matches your overclock plan
Win 7 64 bit (if you want to build now buy vista with an upgrade couplon)
3. Fast Drives - I like WD Caviar Blacks - 640 or 1TB
4. Mid size case with enough room for 5 HDDs (expansion when you want - most will require a back plane in a combined 5x1/4 bay)
5. Mother board that supports RAID 10 and 6 SATA ports and overclocking

I'd suggest thinking about getting 5 HDDs and setting up 4 WD 640s in RAID 10, and use 1 WD 1TB as a back up drive to prevent data loss in the event of an array failure. Set up the OS on a 200GB partition on the RAID array and leave the remainder as a partition for storage of raw files. This way if you have to reload your OS due to virus / corrumption etc you don't loose the data on the storage area. The storage area will have approximately the same room as your BU drive so you can periodically copy the entire drive to the BU one. You can start with just 2 drives and expand later if the budget doesn't allow this to start. The RAID array option will give you fast data feed for virtural memory, boot, and feeding uncompressed data if you choose to use those as an intermdiate.

Tom's hardware offers various CPU benchmarks. For example,

Mainconcept Reference 1.6.1
Video Transcoding: MPEG-2 to H.264/AVC (FullHD Video)

This may not be exactly what you are doing, but is certainly a strong indicator. Note that the Q6600 is about double the render time as an i7-920.

http://www.tomshardware.com/charts/2009-desktop-cpu-charts/Mainconcept-Reference-1.6.1,1385.html

Costco Online has Dell XPS Studio i7's, 12GB RAM, with and without 24" monitor ($1299, 1099). While they only have a single hard drive, there should be a way to get a second one in.

Has anyone used one of the Dell XPS's for Vegas? Any comments?

I have a 2 yr old XPS 720 which is rock solid with Vegas HD editing, Blu-ray and DVD production.

1.5 yr old Dell XPS 420 that I purchased before I got into editing. For the most part it's been really good to me. It had a 2.4 quad and I upgraded to the 3.0 extreme. Upped the RAM some too.