To run vBulletin you will need a Linux OS, we use CentOS on our server (you can download it for free). vBulletin will run on a Windows box but some things just don't work correctly. Been there done that with this site in the early days. Godaddy was surprised that I was able to get it to run at all, just the kinda guy I am,
Also these:
Minimum System Requirements
A webserver with PHP 4.3.3 and MySQL 4.0.16 installed
Recommended System Requirements
PHP 4.4.2 or 5.1.2 or later
MySQL 5.0.19 or later.
You could run a server from home if you wanted. Get a good DSL connection and pay for a permanent IP address and run it that way. Speed won't be the greatest but for 50 or so users it will work. An El Camino site that I'm a member of uses a DSL connection in the owners Auto Repair shop, again speed is not the greatest but we deal with it.