It looks doable in a quick skim through- though if you have specific features that are important, point them out and we can take a closer look.
But Ingmar is dead on- the tricky bit would be importing the forum info. Importing the members would be no big deal- still probably take a wee bit of coding, but wouldn’t be hard. Importing all of the posts and such? Not a small job. You can take a look a this wiki entry on importing phpBB- it’s basically users helping each other through the process. It would give you some idea of the sorts of things you’d face. So- doable, but definitely some custom coding involved. It’s not a small job- you need to have a good grasp on both Simple Machine’s db and EE’s forum tables.