It is also worth knowing that if you know your key for vista you can use any installation of vista to re-install should you have the media from another machine.
Windows will not blindly copy on DELL drivers if the media is from a DELL PC it will copy on only those that are appropriate - then you apply your key to validate the installation.
If you do it a number of times it may require you call the Microsoft help line to validate your not doing anything corrupt - in my experience a quick confirmation of change of machine etc is enough and your given a new key to continue with.