It's not hard to write a quick and dirty script to import a CSV file into a MySQL database. I could provide a simple example, if someone wants it.
As Gardener mentioned, the problem here is deciding what to do about the usernames and profiles. The simplest solution would be to assign all the posts to an existing user.
Another issue is whether the old posts are all separate, or whether they're "threaded". If the latter, the CVS file would need to contain the necessary info for preserving the threads.
The final issue is finding someone with time to actually do this.
