If you are just wanting to restore the machine to a factory state you can follow these instructions according to the manual which can be found at http://support.dell.com/support/edocs/systems/ins2200/en/om/D88330a.pdf
To use PC Restore:
1 Turn on the computer.
During the boot process, a blue bar with www.dell.com appears at the top of the screen.
2 Immediately upon seeing the blue bar, press <Ctrl><F11>.
If you do not press <Ctrl><F11> in time, let the computer finish restarting, and then
restart the computer again.
NOTICE: If you do not want to proceed with PC Restore, click Reboot in the following step.
3 On the next screen that appears, click Restore.
4 On the next screen, click Confirm.
The restore process takes approximately 6–10 minutes to complete.
5 When prompted, click Finish to reboot the computer.
NOTE: Do not manually shut down the computer. Click Finish and let the computer completely reboot.
6 When prompted, click Yes.
The computer restarts. Because the computer is restored to its original operating state, the
screens that appear, such as the End User License Agreement, are the same ones that
appeared the first time the computer was turned on.
7 Click Next.
The System Restore screen appears and the computer restarts.
8 After the computer restarts, click OK.
If you need the actual disk, you can check your warranty here http://support.dell.com/support/topics/global.aspx/support/my_systems_info/details?c=us&l=en&s=gen
by entering your service tag from the side of the machine. If its in warranty you should be able to get a new set shipped to you.
If not, you can contact Dell here http://support.dell.com/support/topics/global.aspx/support/dellcare/contact_technical_support?c=us&l=en&s=gen
and asking for information on replacement disc for your model.
I hope this helps. Please remember to rate this information.