Check the Digi Intelligent Async Adapters category of Device Manager. Your Digi product should be listed there. The serial ports should also show up under the Ports area of Device Manager.
If the adapter was installed properly, the ports should be able to pass a serial loopback test. Instructions on how to perform the serial loopback test can be found here:
HOW TO: Determine if Digi Acceleport Serial Card ports are working in Windows 95/98/ME