The Dell restore will restore the laptop to the same state as when it came out of the box, and should completely overwrite your hard drive. This means that it will include all the stuff that Dell installed at the factory. I don't know about four years ago, but we buy Dell computers here at work and they come pre-installed with Dell Driver Reset, Google Desktop, Google Toolbar, Dell Support utility, and other stuff that we don't necessarily need. The first thing I do when I get these is uninstall a bunch of stuff.
Reformatting the hard-drive will "erase" the disk and then you would reinstall the operating system from a Windows disk. You would need to make sure you have a driver disk for your particular laptop model. You can easily get the drivers from www.dell.com, and burn them to a disk. After installing the OS and drivers, that is basically all you will have installed, none of the other stuff that dell installs, then you just install what you want. This could mean improved system performance as you may have less stuff.
Either way, by Dell restore or reformat, you will probably get rid of four years of accumulated stuff on you drive so you will see improved performance.
If you don't have the Windows disk, Symantic option is probably going to be the way you should go.