I hope someone may be able to give you a more compelte answer as to the specifics of making DB2 work.
BUT - I can give you some general guidance.
1st - you can't mix and match PHP extensions. Any PHP extensions (DLL's) you wish to use with XAMPP have to be compiled for PHP 5.3 (or the version in your XAMPP install), and be compatible with the Apache executables and PHP that XAMPP comes with; that means compiled with the Microsoft VC6 compiler and be od the 'thread-safe' variety. Did that dll you tried meet that specification?
there's a more complete explanation here:http://bravo.newnetenterprises.com/word ... age_id=254
2nd. There are some things that just won't work, (I'm not saying this is the case). Generally if a database is not supported in a suite distruibution -- you are on your own, and that's how the cookie crumbles.
I am personally trying to compile a missing DLL so webmin will again work on Windows with XAMPP (its a Perl DLL that is missing, but the same issues apply)