Using an older version of Xoops would very likely have the same issues AO had. That being, the hosting service using or upgrading to PHP5 and the older Xoops version not being compatable with PHP5.
There should be no problem finding an up to date current solution. The hard work would be in modifying all the display templates to be HTML 4 only. Mostly busy work running down all the templates and not missing one. Though there are just plain simple forums that would reduce this issue.
As for hosting, I'd like to recomend Valhalla-Computers.net. I've had no issues with them and any problems I've had they have worked with me to solve them.
http://valhalla-computers.net/freedom-1-hosting-plan-p-1.htmlDo you know what forum package was used previously? That might be a good starting point.
