How do i restore windows vista from factory.wim?

I have windows vista on a dell inspiron 1420. I have lost the installation cd that came with it

Other options like windows complete pc restore also didn't work as no valid backup locations could be found. But the only ray of hope seems to be the factory.wim file in my d drive. How do i proceed ? Please help. I lost mu administrator password too if it is relevant. Please help as i am really stuck from many a days.