Installing Apache HTTP Server on Vista

Go to Start | All Programs | Accessories, then right-click on “Command Prompt”, and select “Run as administrator”. This will open a command prompt window with admin rights. Navigate to the directory where you saved the apache*.msi install file, and type “msiexec /i apache*.msi” (where apache*.msi is the actual name of the file – hint: type apache and then hit tab, it should fill in the file name automatically).

http://wyome.com/blog/Installing_Apache_on_Vista