I have a bitscope, and from the schematics and info that i've looked at for it, there really is no "magic" going on... it really is as simple as sampling an A/D, storing it in a buffer, and then sending it to the PC periodically. However, obviously the challenge comes in when you look at the operation frequency... the bitscopes are sampling somewhere in the range of up to 40 million samples per second (if not more), so you have to use an A/D, controller (presumably an FPGA or something), and memory that can handle that kind of speed.
My major complaint with the bitscope (besides the software, but that's a whole different story) is that they only used an 8-bit A/D converter.
so if you're going to try to build your own, you should try to use an A/D with more bits :lol: