If you have been into computers and games for a couple of years, and want to play your old favorite games again, you are bound to stumble accross emulation at some point, programs that will allow you to run software for other computers or gaming machines on your PC.
Here at vware you will find the official help file for WinUAE, which is the de-facto standard for emulating Amiga machines. This, however, is just one major emulator I would like to hint at.
Lately, what the developers of MAME accomplished, is simply astonishing. They have the do-it-right strategy which is very impressive compared to most of the projects which just try to make something work, even if it may be with hacks. I recommend checking out blogs of some MAME developers:
It is rather interesting following the progress of these dedicated guys, as MAME is a project that had its 10th birthday this year. For educational purposes, I would recommend checking the source code, as it contains sort of a reference implementation for other emulators.