It might be worth noting (as I performed the upgrade on my mini, 1.83GHz Core 2 Duo, 1GB, 80GB) that the older Mac mini such as mine do not have the right number of antenna's inside to fully work at 'n' speeds. The way round this is to attach the built in antenna to one of the connections on the WiFi card and then add two additional antenna's to the other connectors on the WiFi card. This allows full 'MIMO' - and thus faster Airport transmission rates.
I would show a photo of the two antenna's sticking out the back of my Mac mini, but I am at work and its at home. I'll try to remember when I get back
pac