Click the links a few posts back-- there is a discussion on the method mostly speculation and a video clip on youtube.com
I think he is being secretive (the guy that found it) because he doesn't want to be just another multi million person VC killer but it is possible the trainer is required for that mission.... but maybe not another...
Essentially someone figured out a method to kill insanely fast (30 kills per second) on the PC version of VC...
I have messed around with my game and can't get to the spot he used in the cuban mission "Cannon Fodder" (without being killed)-- but I can almost shoot at the spot where the haitians are spawning from outside the alley... the haitians are respawning very fast after I kill them but have to move into my line of fire so its slower then his rate--- but since I can't aim at the actual spot of the spawn my kill rate is only about 1 per second.... and also my wanted level went up to 3 stars and where I have to stand to get the kills, the police heli can easily pick me off.... it looks to me that the spawn rate can be repeated on PS2 based on what I experimented with so far...
Now if another spot like this can be found in say different mission where you can't be killed or busted---- you can accomplish huge amounts of kills.
The cone crazy trick to make money is a glitch that was sort of fixed for the later PS2 versions and the PC and xbox-- you can still make alot of money, just harder to do.....
Essentially to make a bunch of cash in cone crazy (you can max your money out in about 1/2 an hour)--- complete cone crazy except the last checkpoint.... wait til there is 1 second on the clock and collect it.... you get $200.
Repeat with 2 seconds left on the clock $400, repeat with 3 seconds $800 (see the trend)....
for the 23rd time you beat your record you will get about $838,000,000 which will max your money....
they sort of fixed this for later versions in that they reduced the time you receive for each checkpoint by 1 second the first 6 times you do it.... so you must leave 1 second on the clock for the first 6 times, then 2, 3, 4...etc....
To max your money on the "fixed" verions you will need to get your conecrazy time down to about 8 seconds (I've done it as low as 6 by moving cones around)--- on my original version of VC, beating your record one second at a time will get your time down to 23 seconds when you max your money.... so you can keep repeating to get money but the values will get screwy when they go over $2.4 billion-- due to the number limit on the 32 bit programing they used for PS2.....