Combine new Forum and new help desk on existing site

[zulugogogo]

I am after a combination of something like phpbb and webhelpdesk combined and to use the user login and password from the existing website. The user should login to exiting website and click the tab forum or support. I also want to keep the same style for both the forum and helpdesk as it is with the main site. E.G if I were to change the colour or logo on the existing site it would use the same styles exactly.

Both of the above software actually do what I am after, but I am after seamless continuity throughout the site. Any ideas if there is something out ther already, otherwise i will have to go with the above, but i dont want to reinvent the wheel