1) No – it’s not prepared for bbpress. You need to style the forum tables, etc. – maybe even small php mods are required. If you’re familiar with css it’s not too difficult but it’s a time intensive task.
2) I don’t think this is possible. You’d need to set up a second wordpress installation for bbpress (you can also use the multisite feature) and direct the users from forum.mydomain.com to your bbpress/wordpress setup.