Installing an internal Dvd writer is a simple task - I assume it's a PC and not a laptop ?
After removing the relevant side panel (2 screws usually) , then removing existing CD writer (4 screws), connection of the new unit is a simple reversal. You just need to note how the IDE ribbon cable , power lead and sound lead were oriented originally and replicate that orientation for the new drive.
If you have a look at
http://www.ebuyer.com/UK/store/CD/DVD-Drives, you will find a good range of reasonably priced DVD writers