You can tell if the factory restore partition is still on the drive and still usable by trying to access and try to use it. It has the OS and has all the original software, so you'll need to update. Directions HERE for reinstalling Windows Vista to factory settings. If that doesn't work, you need to do a manual install.You can request a vista disk from Dell HERE You should check with the experts in the Virus Forum first to make sure the infection is completely gone. Even the factory restore partition can get infected with some viruses. 
The infected computer is a Inspiron 530S running windows Vista.  The infection was reported and partially removed by Microsoft Safety Center via a flash drive. I've read "restoring your computer to orginal factory settings" and that seems like the way I should go.  Just need to do two things first: 1)  Buy a stand alone hard drive for backup.  Suggesting on what to buy would be appreciated. 2)  Verify that my system does indeed have the OS hidden in the hard drive.  Would like this verified by Dell but not sure how to do it without paying them for it.  It does have the Microsoft authorization sticker on top. Thank you!
Trojan:DOS/Alureon.A removal