I have a 2000 Taurus with DOHC. If yours is anything like mine, then the work is pretty easy. You will need to remove the throttle body and all connectors to its sensors, such as throttle position sensor, MAF, etc.
Once you remove all obvious, you should be able to remove about 8 long thin bolts that hold the upper plenum. The gaskets consist of 6 small rubber oblong rings that cost about 15 - 20 dollars for the set. You may have to buy both upper and lower gaskets, but they are still not expensive.
You can get the Haynes manual. They have pretty good detail. I did mine in about an hour. However, I'm assuming that the 2003 model is not much different.