Congratulations on being selected as a Intel ISEF Finalist! There is no internet access inside the exhibition hall where the projects are. I doubt there are any exceptions, but if you want to check into that you will need to talk to your fair manager, who will probably end up talking to the ISEF Display and Safety, John Cole. See http://societyforscience.org/isef/rules/safdisp.pdf
for his email address.
Your judges should know that there is no internet access in the exhibit hall and thus should understand that you may not be able to show the complete functionality of your program. Of course, it doesn't hurt to remind them of this during your judging interviews. I think that checking into an offline database will probably be your best bet for showing functionality; ISEF rules and policies are very stringent.
Let us know if we can be of further help!