Hyperthreading is a technology which allows the computer to be working on more than one program (called a thread) at the same time. This differs from the traditional concept of "multi-tasking" because of the following: whereas in a multi-tasking operating system (Windows, Linux, etc.) it appears that multiple programs are running at the same time, they're really not. What's happening is the computer is working on one program for 1/1,000th of a second, then it switches to another and runs it for 1/1,000th of a second, then it switches to the third, etc. So, typically only a few dozen programs are running so each of them receive a large amount of the timeslice per unit time. That makes it appear like they're all running at the same time.
What HyperThreading does is actually run more than one thread at the same time. This has an advantage over single-thread machines (ones without HyperThreading--including AMD's chips), because it is recognized that even in running the most optimized bits of code using all of the resources today's out-of-order execution engines can throw at the it, there are still unused functional units within the processor core. These unused functional units could potentially be used by a second thread. Not always, but potentially. Even if the leftover units are only able to be used 10% of the time, that's a 10% increase in performance.
HyperThreading typically doesn't add much to most code, and it usually eats some overhead to maintain (internally, the operating system must keep track of where each thread is, where it's running, how long to schedule, etc.). It's generally a wash. But, there are instances where it provides significant performance increases (70%+ increase), and other instances where it hurts performance (by 30% or more).
HyperTransport is a bus technology. It is used to transfer data from a chip to other chips or other parts on the motherboard. HyperTransport is multi-ported, meaning that it can be operating several buses simultaneously at full bandwidth.
Generally speaking, a faster FSB speeds up everything. Faster processors only take you so far because nearly everything processor does is fed by external sources, thereby requiring the bus.
