When trying to burn a dvd on iPhoto, the burn failed because of a medium write error..

What brand name of discs are you using?

Are they -R/RW or +R/RW style discs?

How are you burning this DVD with iPhoto?

If you are trying to make a photo slideshow with a DVD,, you many not be doing any of this right.

You may need to use an DVD authoring app, like iDVD, whch is part of Apple's iLife '09 or ' 11 which has to be purchased from places like Amazon or eBay, or Roxio Toast, in addition to using iPhoto.

http://www.roxio.com/enu/products/toast/titanium/

Do a web search for creating a photo slideshow using your particular version of iPhoto.

If you want to make better DVD photo slideshows than what is possible with iPhoto, look at these apps that will give your slideshows more flexibility and a more professional look

http://www.lqgraphics.com/software/download.php

OR

Fotomagico

http://www.boinx.com/