I have a WA4885 emachines system. Its a really good machine with a lot of front panel media plug-ins. It has a DVD-ROM. I wanted to download some videos, I soon realized that my DVD-ROM would not record or burn a DVD disc.
I looked around at stand alone units and plug in units. On a trip to Wally World I picked up a HP dvd 1040i Multi format writer. I've never been inside a computer before, so I was a little concerned about messing something up!
The install was very easy and the instructions were great. The hardest thing was vacuuming out the accumulation of dust "bunnies" inside the computer.
A couple things to remember when you buy a DVD-RW ( or any other add on for that matter) Make sure you computer has the recommended minimum system requirements.
Insure your computer has an "open bay" to install your device. In my case I could have removed the DVD-ROM and installed the DVD-RW in its place. I had an open bay so I left the DVD-ROM in and installed the DVD-RW in the spare bay. My computer already had the plugs for a second device.
Follow the instructions and you should have problems!
Periodically you should pull off the side cover on your computer and vacuum out the dust. The fans especially!
Have fun! Any questions give my a holler! (I ask D1 for the answer!! )

Dust is a bad enemy for a PC it slows down and hampers air flow which is very important to keep your components cool.

Common case building you should always keep the MB risers, CPU fans, all bay covers.

Biggest thing you have to remember about installing a drive or hd drive is setting the jumpers correctly and always ground yourself (touch the metal of the case) and unplug the machine from power. Also there is free software for burning cd/dvd's but I prefer Nero it is a very good package for creating/editing video and files for reproduction.