How old is your Dell comp? They started the factory image restore feature in July 2004. If you bought before that time, it doesn't have it.
Also, you may have to try several times before you are able to get it. I had some customers where we had to restart and attempt 4 times before we got it. Again, wait until you see the Dell logo then keep pressing cntrl-F11, not too fast, not too slow. You'll know when you kick in the utility because the screen changes to "System Restore by Symantec".
No, the Windows System Restore will not work.