How many simultaneous connections can you have with MSDE? Do I need a full blown SS7 to test with multiple connections?

I'm testing an app I developed with MSDE that will be upgraded to SS7 when it goes into production. When I run only one instance everything is fine, if I try to run a second, it waits for the first to be released, then it runs. This applies to 2 instances running on the same machine.

Using 2 machines, I can get 2 instances to start up, but once one has run a query, the second will fail returning ODBC errors from all stored procedures. In case it matters, all inserts, updates and deletes are driven by stored procedures.

Thanx,
Charlie