I don't know if there is a tool like that for Windows, however I do know that since you have your Mail dir saved, that if you were to re-install Linux. You could place the Mail dir back in your home dir, and have KMail use it without any problems.
Also since KMail is in mbox format I think? It might have changed, it's been a very long time since I've used it. Possibly Eudora could read it.