I know this is an old post, but i am setting up the same system, with phpBB 2.0.22, PHP 5.2.1 and mySql 5.0.37. One thing i read is php 5.2.1 doesnt include the extension for mysql anymore. php 4 apparently does. I am still researching on how to add the ext for msql to php . But until i have mssql up and running with a db created and username/password i'm not going to bother with that part. (forgive my terminology i am new to both programs).

I am also having the same problems getting the mysql service to start (xp pro sp2 with all updates install).
I actually got mysql up and running on the first install, but didnt knwo about having to create a db and such until i had started installing phpbb and thought something was broke so i unistalled and fiddled with the instance, then i read up on the no mysql ext deal with php, i uninstalled mysql and reloaded it and ended up getting stuck trying to get the service to start again, so now i have completly uninstalled mysql and deleted folders, etc. I will be trying again in a couple days.

sorry for the long post and horrible sentences but im in a rush to get to bed, lol.

I will post my results of this later, or questions when i am still stuck myself, LOL!

Thanks,
J.C.