In a shell, cd to the directory from which you'd like to serve the site, and rename or delete any '.htaccess' or 'index.php' files, and any directories called 'images' or 'files', that may be there.

Checkout the current code:

svn co http://svn.textpattern.com/current/ .

(Note the dot at the end). To complete the installation, just load http://thesiteurl/textpattern/ in a browser, fill in your database info, and when presented with the config.php block, copy it, go back to the shell client and:

nano textpattern/config.php

Paste in the code block, save and exit (ctrl-x, then y, then return).

Back to the browser, click through, add personal details, and that, as they say, is it.

Whenever you want to update to the latest code, cd to the same directory and:

svn update

...and the latest code will be seamlessly integrated with your installation.