That definately isn't the problem, I used to run a phpBB2 board on a windows server. The requirements for phpBB are:
A webserver or web hosting account running on any major Operating System with support for
PHP
A
SQL database system, one of:
FireBird 2.0 or above
MySQL 3.23 or above
MS
SQL Server 2000 or above (directly or via ODBC)
Oracle
PostgreSQL 7.x or above
SQLite
PHP 4.3.3 or above with support for the database you intend to use. The optional presence of the following modules within
PHP will provide access to additional features, but they are not required.
zlib Compression support
Remote
FTP support
XML support
Imagemagick support
Other free forum software:
phpBB v3
punBB v1
SMF
Vanilla
Premium Software:
vBulletin
IPB