phpBB is native to mySQL... however, phpBB is the ONLY PHP board which aso supports SQL Server 2000 and DSN. If your board is using Access, just use the access DSN when you install phpBB, download both databasees and carefully copy and paste posts, accounts, etc between the two databases. If you're using SQL it's a little more tedious, but is possible...
1. Make sure your ISP has compiled their own version of PHP which includes the php_mssql module. If they've done it, they'll know what you're talking about.
2. Install phpBB using a msSQL install.
3. Export your tables from you old board and do the copy and paste thing into your new board. This will ryally suck, but it's possible. Chances are you'll only be able to save most of your accounts and topics and maybe some of your board data structure (categories, forums, etc.)
4. TELL YOUR ISP PHP BLOWAS CHUNKS!!!
My final guess is that your ISP moved from a win32 box to a nix box... in which case you're screwed. It'd be one heck of a pain in the butt to convert a msSQL database to mySQL.
HOWEVER, if you're currently using an Access database on your board you may be able to use AccessDump (www.intranet2internet.com) to dump your files into a .sql dump file. You could then use phpmyadmin (www.phpmyadmin.net) to import the .sql dump file as a seperate database and carefully move tables, columns, etc into your new mySQL database from phpBB.
Good luck. Maybe consider switching ISPs so you can stay with WebWiz. 
Edited by trendecide