Install XAMPP is simple:
1. Download the zip/7-zip package of XAMPP (I prefer this because it doesn't require installation).
2. Extract it. You can extract it to c:\xampp or other place else.
3. Run setup_xampp.bat
4. Run xampp-control.exe, start apache and mysql
And everything done.
You can now put your php file in /xampp/htdocs to start using PHP.
BTW, stop IIS before start Apache, otherwise your apache will not start.
Hope it helps.