Not sure what to put in the remaining 5¼" drive bay of your souped-up PC, next to the DVD rewriter, 50-function fan-controller/card reader and graphical status display? How about an
audio cassette deck. It plugs into a serial port and your sound card through a breakout box, comes with Windows software for controlling it and recording from/to audio cassettes, and can be yours for a mere US$149 (from ThinkGeek, not surprisingly).