http://support.dell.com/support/topics/global.aspx/support/kb/en/document?dn=1091713
http://www.goodells.net/dellrestore/

The operating system CD maker is no longer shipping on systems invoiced after July 14, 2005.
Your option at point of sale is to purchase the operating system CD for $10. After point of sale, contact Dell and request the CD"
Systems shipped after July 15, 2004 came with Symantec PC Restore. This utility restores the computer to an "as-shipped" condition. If you haven't reformatted, repartitioned, or otherwise modified the master boot record, it should work. Click here for instructions about Symantec PC Restore.

If the Symantec PC Restore utility won't work, but still resides on your computer, a Dell customer has figured out some ways to get it to work again. Note - If you removed this partition, it is not recoverable, cannot be downloaded from the internet, and cannot be shipped from Dell. Click here for ways to fix Symantec PC Restore. Users have also reported that the partition can be restored with Ghost 2003, and Ghost 9 using the '03 capabilities of it. If you boot to the Ghost 9 CD, select Advanced Recovery Taks, select Utilities, then Restore Legacy IMage it should work - but you want to verify the image before attempting the restore. It's in a folder called IMG.

You need a Operating System Install CD - This answer was provided by Dell-ChrisM

Please use the Dell OS Recovery CD program to create the OS CD.
* Click Start- All Programs- Dell Accessories- Dell OS Recovery CD

What if the "Dell OS Recovery Utility" fails or wasn't installed by Dell?
Email or Chat with Dell. Explain your situation and the Dell representative will issue whatever CDs (Dell Media Experience, Power DVD, Sonic MyDVD, Windows operating system) you might need.

* CHAT with Dell
http://support.dell.com/support/topics/global.aspx/support/en/chat?c=us&cs=19&l=en&s=dhs&~ck=mn

* EMAIL Dell

http://forums.us.dell.com/supportforums/board/message?board.id=sw_mediaexp&message.id=2495