HTC and Valve announced the price of the HTC Vive yesterday, and we now know the specs that your PC will need to be able to run it, too.
If you don't want to figure it out yourself, Valve has released a SteamVR Performance Test tool (this link will open Steam directly and allow you to download it). Once you have it installed, the tool will evaluate your system by plonking you down in an Aperture Science testing facility. This is a portion of the demo we've played to test out the original Vive and Vive Pre hardware.
Once the benchmark is finished, it'll give you a breakdown of your operating system, your GPU, and your CPU, and tell you which parts you need to upgrade, if any. It looks like I'll need to upgrade my four year old graphics card before I take the plunge with the $800 headset.
Here are a few examples of the benchmark running on different systems, from our own PCs and collected from these Reddit threads. Keep in mind that performance can vary between runs based on what other applications you have running, an overclocked GPU or CPU, etc. Don't expect an exact correlation between these results and your own hardware.