I don’t think so. Blogs and forums serve two different purposes and I don’t know that anyone has written an exporter to get WordPress blog posts into bbPress.
If you setup that old WordPress blog as an integration with your bbPress installation and then install the bbPress-Post plugin from http://dev.mbzeus.net/forum/ you can do it. It is a real pain in the butt, but if you have the integration plugin working, you can ‘edit’ each of the old posts and then save them again . This creates the entry in bbPress. Last time I checked though, it didn’t update the timestamp to the original post time though.
Speaking of which, it doesn’t add a topic-slug either, which is required to have permalinks set to slug. I tried adding the topic_slug field and a variable to make it update, but when I did that it didn’t work at all Can someone else have a look at this too?