Simplest way to do this is to get hold of an SE923 Barcode engine from Symbol www.symbol.com
The documentation is on-line (large PDF file), This engine has a decoded output, so that all you have to do is implement a TTL Serial interface between the Microcontroller and the 923, and you receive a character stream corresponding to the barcode.
Requires 3.3 - 5V supply, ground, Tx, Rx, CTS, RTS. 12 pin connector but most of the pins are not needed, they are *Redundant* pins from older handheld barcode scanner.
Size is approximately 20mm * 15mm * 10mm so is idea for an embedded solution, they also have a larger decoded version SE1223 which is 40mm * 25mm * 20mm and cheaper in price as I remember.