So what you are saying is that I will get 100% of the benifits of that card that I would get if my motherboard slot were 2,0? I currently have a 2600pro will the 4670 make a difference as to HDTV processing? Is it worth upgrading? I assume 2.0 is for cards not yet on the market?
You will see 100% of the card's power with a pcie 16x 1.0 slot. The reason is that 2.0 just increases the bandwidth to x2 of 1.0. So, a 8x pcie 2.0 slot is just as fast as a 16x pcie 1.0 slot. At this point, I don't know of any single gpu card that actually uses all the available bandwidth of a 16x pcie 1.0 slot, so giving it more bandwidth (going to 2.0) won't matter.
As to HDTV processing, I know the newer cards handle MPEG2, H264, and WMV acceleration. Not sure what else. I don't know if the 2600pro uses hardware acceleration for all of those video types, though.
And yes, most all cards out right now are pcie 2.0, since last year or so. The extra bandwidth will most likely be used in future cards.
PCI-E 2.0 has been around for a while both in video cards and motherboards. Anyway lower end cards don't really make full use of the bandwidth of PCI-E 2.0. There will be a very small performance drop using that card with a PCI-E 1.0 slot, but it's normally a fraction of a percent and thus not worth worrying about. Now if you were getting a more powerful card like a radeon 4870 X2 or a GTX 295 then you would see a small measurable performance difference.