Hello,

I'm desperately trying to use Ventrilo, a VoIP program. Unfortunately,
my ISP has blocked virtually every port the program uses. I need to
find a general range of ports used by this program, so that I can
request they be unlocked. I already know that the program uses
3784/3785 by default, but I'd love to know an approximate range of
ports used by private servers as well.

Thank you very much

You can use any port you want...it is configurable.  Yes, there is the
defaults as you mentioned but I don't know other than that, the port
is purely a choice of the server admin.  The only guarantee is that it
will (ot should be) greater than 1024.