OK -- if you want to stick with what you've got installed (and I assume it's the latest version of Xubuntu), then here's a link to the required package for your Broadcom wireless -- I assume you've probably got the dependencies installed already, but those are also mentioned on the page:

http://packages.ubuntu.com/xenial/admin/bcmwl-kernel-source

EDIT: I just downloaded Xubuntu 16.04, and it would appear that the bcmwl-kernel-source package is actually included on the DVD, so if you have that, then hopefully you should already have all you need -- assuming that your Broadcom device is one that's supported, but I don't see why that shouldn't be, considering that quite a few are supported by the package.

Shouldn't you be able to just install KDE on your xubuntu installation? (It looks like the package is called something like kubuntu-desktop)

Edit: (or lubuntu-desktop, if you would rather try LXDE instead)

How did it all go for ya, dutchbud? Tell us! :)