Shouldn't be much of a problem. Just replace your old drive with the dvd burner. It's just a matter of putting in two cables and your PC will take care of installing it.
Internal:
http://www.newegg.com/Product/Produc...25%20-%20%2450
External:
http://www.newegg.com/Product/Produc...50%20-%20%2475
It seems external is about double the price of internal. If you really don't want to open up your case and you can settle for the double in price go for it but it's like the easiest thing to do to your computer aside from installing ram. The only thing you should be aware of is if it's IDE or SATA. I got a Lite-On drive but recently it decided not to read any CD's only DVDs so I can't recommend them from personal experience.