The program that helps you to get online with Kubuntu is bcm43xx-fwcutter, which is in the repositories.
(Debian link, just to get an idea: http://packages.debian.org/testing/u...43xx-fwcutter)
How to make this as painless as possible? If you install Kubuntu and are able to hook it up to a wired network you could download and install fwcutter. If you want to install it wireless I have a suggestion. For a project I created a "fat" version of Ubuntu with Kubuntu integrated, which has fwcutter pre-installed. It's DVD and even in live mode you can go online wireless. At least you can test it first this way. You can find it here: http://www.linuxtracker.org/torrents...?id=4268&hit=1
It might be a bit too much for you with three desktops (KDE, GNOME and Xfce), but the live version can at least help you to test the wifi card.