Install issues with postgres

Running the install.php I'm getting a BAD Checking PHP support for 
database type: database is not supported by PHP. Check that it has been 
compiled into your server.

I already have postgres installed and am using it for git (which I want 
to integrate with mantis.)

Is this message erroneous in some way or do I *really* need to have 
postgres "compiled into my server"? How would I do that anyway (compile 
into my server)?

Is it possible to have a complete and stable integration of git/mantis 
with git backed by postgres and mantis backed by MySQL?

Thanks,

Bill

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