I have been through all of this, and chose to use the BMW Video module based kit, instead of the aux in with override switch style kit. I felt the integration was worth the extra money.
TVonNAV are great to deal with - I have their video in motion add-on and it's a superb bit of kit.
I bought the video module and loom from newministuff.co.uk, but TVonNAV sell the exact same thing. I bought from the UK as the currency converted to Aussie Dollars more favourably in that case.
Try this link for some more info http://www.mini2.com/forum/first-generation-interior-ice/85601-bmw-video-module-install-pictures.html
I've since purchased a Clarion 4 way diversity antenna with built in booster. The BMW Vid module only has two antenna inputs, so I'm only using half the antenna, but it works well enough. Everyone I spoke to said if you don't have an amplifier on your antenna, you're wasting your time.
Happy to answer any more questions - I've not seen anyone who has done this on mini2 for a long time. woodman438 did a nav-tv conversion a long time ago, but the nav-tv conversion is fundamentally different as far as I know. The BMW Video module approach seems to be the optimum way to do it. The integration is awesome