I downloaded this ISO image, made a DVD and installed it on my Lattitude D600 Laptop as a test.  The D600 is not on the list of supported hardware, but I wanted to give it a shot anyway.  Booting from the DVD warns you that it will erase everything on your hard drive.  In fact you have to type ERASE to continue.  Make sure to backup your important files before booting from this DVD.  This is just a test computer, so I have no data to lose anyway.  Believe me, this computer is no virgin when it comes to OS installs.

If your computer is unbootable, I recommend booting from a Knoppix Live CD.  Then you can backup your important data to a USB thumb drive as a backup.  I didn't have any important data, so I started the default Dell factory installation.  The factory install didn't give me many options besides chosing between an Intel, AMD or NVidia display adapter.  

Here are some screenshots of the installation procedure:

http://linux.dell.com/wiki/index.php/Ubuntu_8.04/OS_Reinstallation

The install took about an hour to finish.  It kind of hung towards the end.  I had Firmware errors repeated throuout the installation.  I have never updated my firmware since I got this computer.  I expected to have a few problems anyway, since this laptop is not on the list of supported systems.  At the end of the installation there were some errors like 'could not open display' and it left me at a command line prompt with root privilages.  Cool!  There was a window that popped up for a a few seconds asking if I wanted to repair the display problem, but by the time that came up I was already pressing the power button to reboot.  It rebooted to the same command line state with the same error messages about starting display.  I could never get back to the window to repair the graphics.  Booting from the DVD again didn't seem to have a repair option, only an entire system install option.  The install finished with errors and no graphical interface.  I wouldn't call this installation a success, but my computer is not on the list of supported hardware.  It was worth a shot and it gave me some good insight into Dell's implementation of Linux.  The lessons learned were worth an hour or so of trial and error testing.  I will still try to fix the graphics problem from the command line, but some non technical users may have problems doing that.

On the other hand, I was able to install the Ubuntu 8.04.02 and 8.10 installation (non Dell) CD's without having the video problem.  The GNOME desktop environment started up just fine with both of the Ubuntu install CD's.  The Ubuntu CD's seemed to have more installation options, instead of being locked into the default Dell factory installation that wipes everything.  I can't really blame Dell for my computers problems, because the Dell recovery DVD was not really designed for this hardware.  I only had 50/50 expectations that it would work with my computer, so I gave it a shot anyway.  

I just wanted to pass on my install experience with this DVD to the Dell Ubuntu user community.  If you have supported hardware, I'm sure the DVD installs just fine.  I'd like to point out that this is a factory install DVD rather than a recovery CD.

Raghu mentioned that he has an A840.  I'm not sure if the Dell Ubuntu ISO DVD image would work on that hardware or not.  If you aren't a computer geek with a few hours to spare, maybe try downloading the Ubuntu 8.04.02 LTS or 8.10 images instead.  At least the Ubuntu 8.04 and 8.10 CD's are a good backup in case your hardware isn't supported by Dell's reinstall DVD.