Oh. You're trying to get it so the computer will only turn on if the coordinates are correct, I take it.
Well, yes, it is possible, but there would be ways around it. So, to get you started on this, I would suggest you take a look at the wiki, specifically the
APIs section, even more specifically, the
GPS and
Rednet sections.
Once you have done that, this will hopefully make a little more sense. You will need to open a specific modem. Then, do a quick GPS call. (gps.locate()) If something comes through, then check the numbers to make sure they are the same. If nothing comes through, shut down the computer. Otherwise, if it has a signal, and matches, the computer runs normally.
Now, this only works if there are other computers to give it a GPS location. Those, I would hide, if you are really worried about people stealing things. Like, bury them underground (shallowly) at different heights with the normal 64-block radius of the modem.
So, that should get you started. If you have any problems writing it, and you have some code, we will gladly help.