> 1) Are there any adverse conflicts between IB6.5 and Firebird in a
> situation like this ... i.e., would running AT against an IB6.5 engine
> ultimately damage the data?

As long as the data file is created and accessed by the IB6.5 server
only no damage should occurr.

The Firebird client lib seems to connect to IB server without problems -
presumably using compatibility to IB 6.0 on both sides.

If your Application does not use any features unique to FB it should run
on IB 6.5.

> 2) Is there some way we can determine at startup time whether there is a
> Firbird engine running or an IB engine? We might want to ensure that AT
> is running in an environment served by Firebird only.

You can use the Service-Api to ask for Server Version info.

Elmar