its called an RNS 510!
£1100 off ebay, with nav info already installed. considering nav DVD is £200 from stealer, thats a big saving.
not sure what you mean by "now as this works of a cd the unit", the data is stored on the internal hard drive, but yes it must have a GPS antenna.
as for antenna, you can just mount it in the dash below the top vent as I did, no need to put shark fin on roof.
one thing you cant do on an RNS 510 (and we cant find a fix for it yet) is to enter a full UK postcode. strange but true.
loads of info here:
www.vwnavi.com