A dvd disc holds around 4.7 GB of data which is a huge amount (2 hours of sd quality television)
If you were using a dvd recorder simply reducethe recording quality and it will fit. As you are using a pc though, you will need to use dvdshrink to squeeze the video ont the disc.
Dvdshrink is freeware and will not cost you anything to download or use.
I would look to see how big the original file is first as a music video is usually only 3-4 minutes long and should easily fit onto a new dvd.
A dvd RW will need to be formatted before using or
re-formatted if re-using one that already has something on it . This will wipe off what was on the disc before.
http://www.dvdshrink.org/why_en.php
download from here should take a few seconds
http://www.afterdawn.com/software/video_softwa re/dvd_rippers/dvd_shrink.cfm