Hi!
I've recently written a php-module that does database abstraction (like the pear-stuff, but in C).
It only supports MySQL and ODBC now, but is easily extended to other databases (if you know C, that is).
It is freely available, (hope you don't mind the plug :-) at http://www.guidance.nl/php/dbx, including source, user docs and developer docs.
It works on both Linux and Windows, may require re-compilation, but full source is included.
I'm using it myself for some projects, and though I only use MySQL databases, I find the functions easier to use than anything else that's available. But then again, I wrote it myself, so it should :-)
The module works 100%, but some user-input to make it better would be most welcome. You can mail me with any questions you have about the dbx-module.
Cheerio, Marc.