Uninstall vista and reinstall xp

If your Vista was Vista Professional or Vista Ultimate, they grant free downgrade rights, so a retail purchase of XP would not be needed. If it was Vista Home, then you would need to buy a retail version of Vista, as the previous poster said. Note that the allowed downgrade is to XP Professional.

Even IF you get the software, you would need to make sure drivers are available for XP with your computer.....

If you are still under warranty you can call Dell and see if they will send you XP, or you can go out and buy the retail version

My comp came with windows xp on it and the vista came with as a upgrade I waited 3 years to put the vista on my comp now I hate it and want it off and my original comp with windows xp back on it.

Here are two different web sites with information about how to install Windows XP:

http://www.theeldergeek.com/clean_installation_of_windows_xp.htm

http://www.microsoft.com/windowsxp/using/setup/winxp/install.mspx

But how do I get the windows vista off in order to put windows xp back on and I don't have the product key info for my windows xp I have misplaced the disc cover for my windows xp disc.

If your computer came with Windows XP then hit CTRL F11 at boot when you see the Dell logo. Then you can restore the original image that was on your computer when it was shipped. Doing so will erase all data so backup what you need to before doing this. If it fails then you can request backup XP cd from Dell. 

If it were only as easy as that it would be nice.  I'm not sure what was required to get the Vista upgrade onto the hard drive, but it for sure wiped out the special Dell MBR required for CTRL_F11 to remain functional.  At this point the only way to reliably get Windows XP onto the hard drive is to perform a clean installation as suggested by hrova earlier in this thread.  If you enjoy learning about computers you may also be able to repair the CTRL_F11 process; you would need to study this page:  Inside the Dell PC Restore Partition by Dan Goodell.  This would depend on being able to find the partition containing the PC Restore image; hopefully the Vista installation process left it in place.

If the computer came with Windows XP you should also have received the Dell Resource CD for Windows XP.  This would have the Windows XP drivers for the E520.  You can also get the Windows XP drivers from the Dell support page.  The E520 may be new enough that typing its service tag onto the Dell downloads page would bring up the drivers that were loaded onto your E520 when it was delivered.

Yes just found out that my f11 is not working with the windows vista. About a month ago I decided to install the windows vista home on my E520. After installing it and trying the windows vista I do not like it and want to remove it and reinstall my windows xp. Well I am trying to remove the windows vista and can't. Need help. I do have the Dell Resource Cd for Windows XP and have the original XP reinstallation Cd but if I ever get it reinstalled am I gonna need the product key for the XP installation and if so I have lost it. 

In order to install Windows XP you will need to boot from the Windows XP reinstallation CD that came with your computer.  Provided you are using the Dell labeled CD there should be no need to type the characters on the COA since Dell Windows installation CDs are pre-activated.  Once you have booted the CD and selected the option to install Windows XP you should eventually reach a point that you are allowed to delete and create partitions.  You will need to delete the partition containing Vista; this should be the largest partition on the hard drive, formatted as NTFS, and may be labeled "C:".  Once you have deleted the partition you should be able to select the option to have setup install Windows XP into the resulting unallocated space.  Windows setup will then re-create the C: partition, format it, and install Windows XP.  Refer to the links in hrova's post for detail.

When you have finished installing the OS, install the drivers one at a time.  You need to install the first two in this order:  Desktop System Software and Intel Chipset Driver (sometimes labeled as Chipset Installation Utility).  The order of the remainder is less critical, but due to the resources required Dell recommends that you install the video adapter, network interface adapter, and sound adapter in that order before anything else you may have.

If your system came with XP installed there should be an xp serial key on the case itself. It's usually located on the case top, back panel or side. Just take a look all around. Good Luck.

It did come already installed, but that was 4 years ago and have since misplaced the disc envelope that it came in with the product key on it. Only decided a month ago to install the windows vista on my system, but do not like it and want to remove it.

I cannot get it to boot from my windows xp reinstallation cd it keeps rebooting to the vista screens.

What procedure are you using to boot the CD?  There are two.  One has you go to setup (F2 during the self test screen after start) and set the CD ROM drive to be first in the boot order.  If you place the CD in the tray after having done this you should get a message on the screen to press any key to boot from the CD ROM drive.  The second has you press F12 during self test after start and brings up the one time boot menu.  Once you have selected the CD ROM drive as the boot device you should see the message about pressing a key.  If you wait too long to press a key the computer will try to boot from the next available device, usually the hard drive.

Another thing you should keep in mind; some of the computers that have SATA drives still use the older IDE controller for the optical drives; CD and DVD.  If you have two optical drives and have had no luck with one, try the other.  Only the drive on the master connector of the IDE channel will support booting.