Since its a Duemilanove, its an entirely pointless exercise anyhow, theres already a correctly wired LED with resistor on the board for pin 13.
The real problem is that there are many out of date tutorials on the internet from the Arduino NG days which didn't have an LED already connected but did have a series resistor on pin 13 and it was accepted practice to just plug an LED straight in. Noobs just blindly follow 'em.....