Local Installation

I am trying to do a local installation on my computer so I can mess around with themes, etc. without hoarking up my main site and am completely baffled. I have installed xampp locally and can access it. I have created a WordPress database in xampp. I have copied the required files to the htdocs folder in xampp (lite). I have changed the config-sample file to reflect the local host, database name (wordpress) and blanked the password as covered all over the web and saved the file as config. I keep getting the following when trying to install:

Warning: require_once(./includes/upgrade.php) [function.require-once]: failed to open stream: No such file or directory in C:\xampplite\htdocs\wordpress\wp-admin\install.php on line 10

Fatal error: require_once() [function.require]: Failed opening required ‘./includes/upgrade.php’ (include_path=’.;C:\xampplite\php\pear\’) in C:\xampplite\htdocs\wordpress\wp-admin\install.php on line 10

Can anyone point me in the right direction? Is there another version of WordPress other than 2.5.1 that will work?

Thank you,

Scott