You do need the code. If you have Vista installed now and working, install a program called Belarc Advisor. It will tell you your system specifics in a web browser and give you your Vista Product Key, save it somewhere.
Do I need the Vista product code key to re-install Vista Home Premium x64 SP1, from the Dell re-installation DVD which came with the laptop Dell Studio 1537?  The code key tag came off the bottom of the laptop and is lost somewhere along the way.   Thanks Joel727
re install Vista