...is quite simply: don't. Or at least don't use it at the beginning.
I've found that by using it, I have only been able to collect 99 out of
100 packages. One disappears, and it appears to be random. The first
time I tested it the package behind the billboard (at the airport) was
missing. The second time, the package in the orange shower stall was
missing (across from the hardware store on the east island).

I'd recommend those folks to start a game as normal, then once they have
all of the packages, then use the GameShark. Though I can't say for
certain that other problems won't arise.

The best strategy I've found is:

Start a new game and don't do story missions. On the east island, do a
bunch of cabbie missions until you have $14,000+. Cabbie missions are a
great way to get some quick, safe, cash, because for every five people
you drop off you get a bonus doubled by $500. Then, grab a ambulance and
run over to Pier 1. Back it up so the back is facing the fence. Hop onto
it, then over the locked gate. Grab a boat and cruise over to the west
island. From there, make your way to the Hyman Condo and buy it. From
there you have a save point, and a helicopter right on top. Though I
think a good tip is to save per every 5-10 packages, just in case your
helo blows up.

For everyone else, this is old news. Don't mind my post. :)

-Will