The default webapp uses jsf, but the difference is not that big. Look at the TaskBean and the HomeBean with the corresponding jsp's. If you know your way around struts, you should be up and running in a few hours.
afaik runa-wfe has a struts wrapper around jbpm, but for 2.0 afaik. Their code is also open, so take a look there as well.
i regret the fact that RUNA is not interested in combining our efforts. now, they duplicate quite a lot of effort. if they would become a partner and collaborate on the same platform, we could both get a lot more value, i think.