Webmatrix does not recognize already installed MySQL and PHP?

I have recently installed Webmatrix and promptly stumbled into a problem. I have already installed PHP (5.2.16) and MySQL (5.1.40), both work fine for sure. But Webmatrix does not recognize either of them:

• <div mce_keep="true">When I attempt to establish a new database connection, Webmatrix only offers "SQL Server 2005/2008" even though I read it everywhere that Webmatrix fully supports MySQL.</div>
• <div mce_keep="true">When I attempt to enable "PHP support", Webmatrix insists on installing either PHP 5.2.x or 5.3.x eve though PHP is already installed.</div>

Does anybody know a solution to this problem? I do not really feel safe reinstalling PHP and MySQL just because Webmatrix does not recognize the installed versions - who knows what Webmatrix will install?? BTW, I am using Win XP Pro SP3.

Any hints are appreciated.

Torsten