Hello,
This is possible, but you'd need to have the domain on a hosting account such as one from
www.godaddy.com (providing they'll let you have emails for your domain. They do, for a monthly cost I think).
Then, you can park your domain (in the upgrades tab in your ACP) to your forum.
If you're interested in doing this let me know and I'll post the steps for how to do it
