I want to set up a XML service that will act as a middle tier between
several different client apps and a rather expensive and outdated ODBC
client.

Currently, wehave several machines with an particular ODBC client
installed so that these machines can access a UNIX accounting systems's
core tables directly.  But the problem is that we have only 3 access
license; in other words, while we're free to install the ODBC on as
many machines as we like, only 3 programs can actually be connected to
the UNIX db at any given moment; attempts to go about that result in
failed calls.

So, what we'd like to do is introduce an XML service that uses a single
ODBC client seat, and then all other apps would be upgradeed to use the
XML service.

My question is this: how do I set up some kind of FIFO within the XML
service, so that it can queue multiple requests from any number of
applications.  Is this taken care of automatically by IIS, or will IIS
attempt to open any many connections to the ODBC as it can, rather than
one at a time?