you will need a bigger hd also best to upgrade your memory to 512 and install a good graphics card.installing the dvd burner is ok it is what you are going to do on the computer that needs the extra resources.Regards
It's best to have a hard drive especially for your video/DVD work. 40 GB is an absolute minimum for all the extra space and files needed for processing. You can, of course, clear it all out before you do another project.
As hard drives are so cheap at present, get one as large as you can afford, say 80 or 120GB and your processing is then less likely to suffer from video "constipation".
If you're adding menus and chapters and such like, you will need software. We're just starting small scale pro video work and have bought Pinnacle Studio 9 as a tryout before going on to more highly specc'd programs. It's very good and quite comprehensive, so much so that we're delaying buying the expensive stuff.