Wireless on my MacMini (1.5Mhz edition) have been working for quite a while now, cant remember from which version it started to work. But perhaps they did use different wifi chipsets in some models?
I don't think there are different chipsets... I think all internal wireless interfaces should already be supported in Mac minis, IBooks, and PowerBooks. Only thing that some models didn't come with internal WLAN by default. All 1.5GHz minis came with Airport, but lower specced models had it only optionally.