In Vista you need to be logged in as an administrator and to also disable UAC (User Account Control) as it restricts certain administrative function necessary for the smooth running of a web server - you will be a web server administrator after you install XAMPP.
Install XAMPP to the root of a drive or partition, for example to the C:\ drive so you end up with all the installation files in C:\xampp - do not install XAMPP to a folder with a space in the name and remember that all things in XAMPP are case sensitive.
To disable UAC go to
Start>Control Panel>User Accounts
there you will find an option
Turn User Account Control on or off
just click on it and uncheck
User Account Control to help protect your computer
click OK.
If you also have IIS installed and active then you will not be able to run XAMPP on port 80 and SSL on port 443.
Simply disable IIS as you won't need it if you install XAMPP and Apache.
To disable IIS go to
Start>Control Panel>Programs and Features
on the leftmost side you will find an option
Turn Windows features on or off
click on it and uncheck
Internet Information Services
click OK
and then restart your computer.
Good luck Floyd!
