i actually had the rcd 500 6 disc jobby with soundpack, but the 510 will fit most current (within last 3 years or so) with no problems at all, and yes i have highline, i got mine from czech for 1000 euros, about the only shop i know that has them is
http://cgi.ebay.co.uk/New-VW-Golf-Mk5-Eos-MFD3-RNS510-RNS-510-Navigation_W0QQitemZ370041127646QQihZ024QQcategoryZ156954QQrdZ1QQssPageNameZWD1VQQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247
but be carefull and check they have stock as they didnt when i checked but still had the ebay advert up

Edition 30 • Candy White • Lux pack • Front Armrest • ipod • Tinted Rear Glass • Multifunction Steering Wheel • Highline • Sunroof • Zenons • Soundpack • Cruise • Rns510 Nav •