dotnetnuke rdoes not use php. It equires asp.net 2.0, and by default supports sql2000, msde 2000, sql express and sql 2005 . There are a number of alternative data providers available such as oracle (and I believe mysql), but AFAIK they're all commercial ones i.e. they cost money. I would suggest you get a different host, one who does windows hosting, or else look at a package aimed at php/mysql such as mambo or plone.

Cathal