Short bio: Computer Scientist, FOSS supporter (read more)
Tux Machines (TM)-specific
One of the sacrifices I had to make when choosing to install Ubuntu 8.10 was that there would be no way to turn off wifi and bluetooth. The battery would drain faster because I would have to keep them powered when not using them.
Dell released Aircraft Manager, a program for turning these devices off, in lpia form for Ubuntu 8.04 when the Mini was first shipped. Seeing how I was not running an lpia system I was hesitant to install the package. Recently it was brought to my attention that there is a Aircraft Manager.deb usable in both i386 and lpia systems.
Once, installed you can find Aircraft Manager in System>Preferences, under the title Airplane Mode. It allows you to turn off wifi and bluetooth.