Can't really help you on Demolition Man since I never technically did the mission "myself."
For Supply and Demand, you just need to race those other boats to the Marquis(?) Don't rush it because you could lose control in those tight turns near Leaf Links. It'll take a good while for the other boats to reach it. When you have to shoot, aim for the explosive barrels when you face the guys on foot. The boats shouldn't be much or a problem.
For that guy on the Securicar in Autocide, just try to shoot from a long range away from them both and if the guy drives off in the Walton, just chase after him and do a drive-by on him.
I'm a little shaky on the Vice City missions so forgive me if I'm a bit inaccurate on some things.
Mump. Not really related to Euro 2008, so I post it here.
I heard Christiano Ronaldo is going to leave Manchester United for Real Madrid with no hesitation. What you think, widespread Manchester United fans on this forum?
Out of Downtown, Little Haiti, Little Havana, Viceport, Vice Point, Washington Beach, and Ocean Beach, which two parts of Vice City don't have an asset property?
What is the weapon in the explosive category that is only available on the PS2 and not the PC because it causes frame rate issues? Hint: Spawns in back of the Washington Beach Police Station.