Having just recovered a laptop from a very serious Virus infection, I also had to reinstall the original dell image. 
However, after spending a lot of time trying to follow the instructions on various sites I gave up and followed my gut insticts (I have been repairing computers for family and lots of 'friends' so I am not a novice)

So here are my guidelines for restoring a Dell:

1. You will need access to the Internet so get a friend or use another computer to get a copy of Imagex.zip. I cannot link to the place I found it as I am not sure of the copyright issues. (search google though)
2. Unzip it and you will find 2 files. Save both of these to a flash drive so that you can use them later.
3. Use a BART PE disc to boot the the broken laptop/computer into an XP session. If you don't have a Bart disk then again use google to find it.
4. Once the computer is up and running, use 'file explorer' to find the RECOVERY partition.
5. Look around this partition to find the file called 'factory.wim'
6. Copy the two files you got earlier from your flash drive to the same place as the 'factory.wim' file
7. Now using Explorer, find out the drive letter of the hard drive which you are going to reinstall the image on to.
8. Open a Command prompt window.
9. Now type in the following - change the last bit (c:\) to whatever drive letter you found in step 7:

imagex /apply factory.wim 1 c:\

Hopefully after a short time you will have a functioning computer again.