TEMPLATEPATH without the theme name? No THEMEPATH constant?

dirname( STYLESHEETPATH );

That will return the theme directory.

Never assume /wp-content/ below ABSPATH. I’m using often a different directory and domain for wp-content to enable cookieless requests to theme files. Bad plugins and themes break terribly in such cases.

Addendum

Or use get_theme_root() for the file path and get_theme_root_uri() for the URI. Both are defined in wp-includes/theme.php.