Schematics for USB Adapters

Anybody know where I can get a schematic to build a Serial -> USB adapter? I got a new computer with USB ports but no Serial port. I’d rather not spend the $$ on a new serial port card or a hub with the serial port on it if I can avoid it. $60-$70 is a little steep for something I’m not going to get much use out of.

While we’re at it, how about a schematic for a Game/MIDI Port -> USB adapter as well? I’d like to hook up my MIDI keyboard but my soundcard doesn’t have a Game/MIDI port on it. 🙁

TIA