2oodlez, I'm not sure if you are still having a problem with this or not, but I have a few questions if you are.
Does the drive read any type of disk at all (CD audio, program disks such as for MS Office or the Windows reinstallation CD)? If it reads CDs but not DVDs then it could be a problem with the reader portion of the drive, which would mean replacing the drive. Since you are in warranty, it should be a simple matter to have a replacement set up (either sending the replacement drive directly to you, or having a tech come out and do the work).
If it sees the drive, but doesn't read any disks at all, then it gets slightly more complex. I could still be the drive, but it could also be software settings in Windows itself at that point. The easiest way to check is to delete the drive from Device Manager (Control Panel > System properties > Hardware tab > Device Manager button then right click on the drive in the list and select Remove or Uninstall). Once removed from Device Manager restart the computer and wait for Windows to detect and reinstall the drive. If it is just a software problem that should fix it.
If you have any questions about this, or are still having problems with the drive, feel free to let me know and I'll be happy to provide additional help.
Dell Customer Advocate