You won't have much luck installing JForum on most of the common hosting companies (i.e. 1 & 1, GoDaddy, etc.) because they do not offer a
Java app server. GoDaddy claims to support java, but it's really just for
applets, not full java applications.
If you pay to have your own virtual or physical server, you could install tomcat or some other app server.
There are a few places that do offer java app servers as part of "shared hosting," but they tend to be more expensive than the "non-java" hosts.
[originally posted on jforum.net by GatorBait3]