Askbot is itself a Django app, but it does require quite a few config variables in the settings.py file, so the easiest path might be to install askbot as a standalone django project and then add other apps that you might need.
Second part is setting up askbot at sub-url - there is setting ASKBOT_URL - make it equal forum/.
Lastly - if you need to serve something other than django project at the root url / and still host Askbot at sub-url - then find instructions by looking for "hosting django at sub-url" there are good hits on google for this.