Database Abstraction Suite

Hi all I am busy developing a PHP DB application. I obviously want this to be as portable as possible - and then went to the Zend pages. I have looked at the DB abstraction Applications. There are five or so which have all been rated as a four dot (I presume out of 5). Does anyone have any experience with DB Absteraction suites. If so, I need one that supports InterBase/Firebird and also supports MySQL. I would like to know what they are like in terms of ease of learning the generic things, etc, etc. Thanks in advance David Russell