Thanks to the wp-hackers list I came across a plugin called Slave Me WordPress. It allows you to use the user tables from one WordPress install in another install. So you can add a second blog to your website but keep the same user logins.
Using this plugin, you can use TDO Forum to add a forum to your WordPress blog. Like I’ve just done! My new forums are actually powered by WordPress with the TDO Forum theme. Please feel free to try it out. If you’ve registered an account on thedeadone.net, it’ll be valid on the forums. I was afraid TDO Mini Forms plugin might be incompatible with Slave Me WordPress plugin, but it isn’t, which is exceedingly cool.
I did have to write a new plugin that converted my old forum posts (from XD Forum) into actual WordPress Posts and Comments. I’ll be releasing that plugin during the week btw. I’ll also be making a new release of TDO Mini Forms (several bug fixes) and TDO Forum (with a custom posting interface). So stay tuned!