Hi Steve,
Probably the best idea would be to just do some heavy reading of the forums, especiallyy the AV Recievers forum, the speakers forum and the DVD Players forum.
Also, have you got an AV system yourself of any kind? If so, what are the tech specs - have search for the name of each spec and get an idea what it all means. Take a look at the glossary section of an av manual and get familiar with terms used.
Perhaps buy yourself a copy of a popular AV of hifi magazine, perhaps Home Cinema Choice or What Hifi, something designed with the beginner/intermediate hifi buff (ie, not too heavy).
That'd be a good place to start. By the way I'm probably going to move this thread to the General AV Chat forum soon as feel that's the ideal place for this thread.