Found on YouTube: Vice City on Commodore 64?
As part of The Majami Hiroz Show channel on YouTube (pronounced 'miami heroes' - a nostalgic "Welcome to the 80's" themed channel that pays tribute to 1980s music, movies and games in the form of original 8-bit homages), we stumbled upon their latest entry: "GTA: Vice City - Final Mission (C64 Version)".
An awesome little re-imagining of the denouement of Grand Theft Auto: Vice City, "Keep Your Friends Close" - the bloody grand finale shootout at the Vercetti mansion rendered as a believable 1980s 8-bit arcade experience complete with midi-style audio, vintage pixel effects, and other appropriate trimmings.
Spoiler alert: if you never actually finished Vice City, you might not want to have the ending revealed to you through this 8-bit depiction - in which case, we recommend finishing up those old affairs properly.
Otherwise, do enjoy: http://www.youtube.com/watch?v=XVHqL_uTqOg