Licensing in multi-tier environment

Hi everyone,

I have two questions:

1. If you take this setting: InterBase 6 server and one Delphi app on the
same computer connected to the server, acting as a data provider for about
20 remote clients (also Delphi apps) connected to the provider using MIDAS,
how many client licenses do I need to pay - only one, because only the data
provider is actually connected to the server as a client; or do I still need
to pay 20 client licenses?

2. On the Inprise's online shopping site I found this (regarding InterBase 6
pricing):
    - Server license 1 user - $200
    - Simultaneous user license - 1 pack - $150
What is the difference between the two, and what do these exactly mean?

By the way, is the Open Source version reliable enough to be used in this
kind of environment (question 1), working 24h a day, 7 days a week
(stability is an important issue here) ?

Thanks,
Nenad Konstantinovic