If you want to install Ushahidi on a XAMPP stack on windows (my installation has benn tested on a windows 7 professional 64 bit) you have to:

1. install the XAMPP stack on your computer: http://www.apachefriends.org/en/xampp-windows.html#521
2. check the System Requirements here: System Requirements for setting the cURL you need to uncomment the line: "extension=php_curl.dll" in your (that is the default location) \xampp\php\php.ini file
3. unzip the Ushahidi folder in the web server root (default is: xampp\htdocs)
4. create the Ushahidi database via Phpmyadmin
   to use Ushahidi's "Clean URLs" feature (and if missing add it) read: System Requirements (the default location of the Apache configuration file is: xampp\apache\conf\httpd.conf)
   install Ushahidi: go to localhost/ushahidi and follow the wizard: