Here's a good LGPL library for encoding QR code libqrencode
Libqrencode is a C library for
encoding data in a QR Code symbol, a
kind of 2D symbology that can be
scanned by handy terminals such as a
mobile phone with CCD. The capacity of
QR Code is up to 7000 digits or 4000
characters, and is highly robust.
Here's a Google code project that decodes QR code - aimed at iPhone, but is LGPL and the source is available. Should be adaptable...
-Adam