alright ive got a solution for you. theres a website that makes savegames after EVERY mission for gta's (gta3, vice city, san andreas) so your problem is solved.
all you need to do is click this link, then a savegame will download in a winzip file. then extract it, and put the files in the folder in my documents named GTA Vice City User Files
now you have a savegame for vice city with demolition man completed