seems i have found a hidden room. it'd be pretty suprised if it hasnt been found yet but anyway. I used the jetpack from the Ultimate GTA Vice City trainer by LithJoe jet pack to get there. You'd need this trainer or atleast the jetpack mod from the trainer to enter the room.its in little haiti near kaufman kabs. its that staircase that goes down to those doors that has a hidden package on it. Inside the room there is a printer and what appears to be a small door or a locker. there isnt anything past these doors. here are some pics:
