If I buy a PCI-E v2.0 graphics card (Nvidia Geforce GTX 275) will it work correctly and to the full potential with my PCI-E v1.0 motherboard (Asus P5B-Deluxe) ?
Solution:
Yes. PCIe is backwards-compatible, so you can use 1.0 cards in 2.0 motherboards and 2.0 cards in 1.0 motherboards.
As to reaching the full potential of your graphics card, it’s true that PCIe 1.0 is half the speed of PCIe 2.0. (So a PCIe 1.0 x16 interface is comparable to PCIe 2.0 x8.) But single graphics cards really don’t saturate the bus anyway: if you dig around through older tech articles, you’ll find a number of reviews of video cards in the x8 PCIe slots of early SLI/CrossFire motherboards. Invariably, the conclusion was that the slower bus didn’t hurt performance noticeably at all.
You’ll be just fine.