My wife has a Jul 04 Mini One with ISOFIX.
We have been using Maxi Cosi Cabriofix with the Quinny Speedi SX pushchair - the Quinny goes, with rear wheels removed, into either in the front passenger seat (with a seat cover to protect the car seat or in the back with one rear seat folded down. If the former, tape carpet or seomething else to protect the side of the console by the ashtray from scuffing.
Carseat Brand: Maxi-Cosi
Carseat Name: Cabriofix
Attachment method: Isofix
Childs weight: birth to 9kg
Childs age: birth to 9 mths approx
Carseat weight range: Group 0, see above
MINI Type: One
Body Type: Hatch
MINI build date: important as there are variations
Interior trim: Standard
Cheers
TT