[ gpsdrive ] Two Questions....

Greetings Everyone...
        I'm really impressed with gpsdrive and learning more and more about it
everyday.  I am also thankful in advance for the expertise of the
members of this forum and their willingness to help.  That said, I have
two questions.
        First, I have downloaded a map of the Bratislava, SK, area where I live
and work.  However, when I have my Garmnin eTrex connected, it shows my
current position about 10km north and slightly east of my true position.
How can I correct this?
        Second, I'm encouraged about the possibility of using gpsdrive with
Google Maps.  Is there a tutorial somewhere on how to do this?

Thanks in advance,

Paul in Bratislava
Homebase in Carlisle, PA, USA