Unfortunately (or fortunately, if you're looking at it from a privacy standpoint), web browsers disclose very little information about the underlying platform. The most you get is browser & version, OS & version, and maybe what CPU architecture. All that is easily spoofable.
I guess you could try to use a Java applet, but they have a reputation for being hugely insecure. About the only thing that I can see working would be a skinned CPU-Z that validates to TH servers and automatically ties it to your username. Probably not cheap.
It would also have to be entirely opt-in, because there's a good chance that people would either be running an unsupported OS (e.g. tablet), or don't want to run reasonably untrusted software.