Guillaume Plessis has updated the DotDeb.org PHP 5.1.2 packages for Debian

Changelog:

php5 (5.1.2-1.dotdeb.2) unstable; urgency=low

  * PDO support added (MySQL, SQlite & Postgre)
  * PEAR include_path is now good by default
  * Added missing libsqlite*-dev dependencies
  * Added missing apache2 dependency

Here the apt source for /etc/apt/sources.list:

deb http://packages.dotdeb.org stable all
deb-src http://packages.dotdeb.org stable all