> I need to know if its possible in either Interbase or Firebird to
> prevent any user account to create databases...

I prevent it by introducing an additional step before "real" login into
FB/IB. It's providing a simple remap of user's password with a secret one
(which is unique to all registered users in fact). User name will be kept,
so USER variable will deliver same result. This allows me to deploy database
to other sites and to set up new accounts to isc4.gdb automaticly...

Mit freundlichem Gruss & Best Regards
Andreas Pohl
ibp consult