Well, good news is setting up an Openfire server from scratch is dead simple. The most involved part will be either re-creating their user accounts or setting it back up to use LDAP (Active Directory presumably).
There’s a few threads on this forums as well as some docs on how to do the LDAP setup (I haven’t done it myself, my company uses openfire user accounts instead of ldap ones for login).
If they don’t have any special configs or setup, then I’d say you may be best off just setting up a new server fresh. You can set it up to import the users from the correct OU in your LDAP just like before, or use the “embedded users” that you can create directly from the openfire web gui.
The embedded database vs. “real” database depends on your scenario. The embedded database is easy, and requires no additional configurations to get up and running. The downside is it may not scale with large deployments. In that case you may opt for something like MySQL or SQL Server as the database backend. This requires a little additional work, but is also easy (follow the guide that comes with your Openfire download, there’s an entire section on database setup).
Windows Server by default has the firewall disabled, so you don’t necessarily need to worry about correct ports, etc.
Good luck! Post back if you have problems still, plenty of folks on here use Windows as their server of choice (why? I don’t know… sigh), and many others have done teh LDAP route.