I must point out that I will:

http://blog.davejamesmiller.com/2011/03/how-to-install-php-5-2-fastcgi-on-debian-6-0-squeeze

(Copy HTML zipped: PHP52_on_Squeeze.zip )

There are clear instructions and simple to install PHP 5.2 on Debian Squeeze without downgrading global PHP5! In other words, in this way you sit quietly on the same server both versions - the 5.3 with the 5.2 - addressing the many problems introduced by the change in basic version for web applications like Drupal 5 .* on Squeeze it refuses to run, As many know by now - at his own expense ;-)