prioritzation of resolving dns queires

[Wade Grant]

I have situation that needs resolution.  I run a split DNS setup and
yesterday I lost connectivity from my ISP beyond the perimeter. 
Suddenly the internal DNS pegged out on it's processor due to it not
being able to resolve outside addresses. This happen at a peak time for
us and I could not get users to access internal systems through DNS
resolution due to the DNS being overloaded with requests for outside
resources.  How can I force the server to manage queries so that
internal record request take priority over everything else?
any suggestions would be appreciated.
wade G.