This Excel workbook will let you generate and print out a valid, scannable EAN-13 barcode. Uses no VBA, no macro, just a lookup table and some conditional formatting. It ain't pretty, but it works.
No checking is done on the 13 digit number you supply, so you will need to calculate your own check digit.
This was a 10 minute quick hack after I took a look through the EAN-13 specs.