Different web hosts run different servers, different servers support different technologies. Findout what your web site supports then look for software that corrisponds to the server your site is running on.
If your site runs on a Windows IIS web server it should run ASP and so should run the forum, unless your hosts have disabled it. If your web server is a Unix web server then it will probally be runnung Apache web server and so will more than likly support PHP, in which case you need to find software witten in PHP.