Introduction to Hyper-Threading
Intel has a web-based tutorial on their new Hyper-Threading Technology (HT Technology) entitled "Introduction to Hyper-Threading", which tells you how the technology works and how you can exploit it in your software.
Hyper-threading is an advanced processor design technique that allows a single processor to run more than one code thread simultaneously. It takes advantage of the fact that not all "units" of the processor are simultaneously in use when executing a single thread.
Please note that HT is rather different than the new "dual-core" chips that are coming out. The latter actually have two completely distinct processors ("cores"). It's not clear to me whether each of Intel's dual-core cores also support HT.