Help using gps!!

Hi everybody,
i need your help friends,
im in dominican republic the ph comapny that i use is orange and i want to use the gps of my G1..
So when i go to google maps app. i put the address where i am and then i put the address where i want to go the results are that no route found..

Pls. can somebody tell if im doing something wrong or if i have to download any specific app. or what pls help

i will really appreciate your help...