I think the problem may be in where you are expecting to see "Active Sync" show up as a service. From what I am reading, you are looking for it in the settings for your Belkin device, but you should be looking for it on your MDA.

For the Belkin device, all you need to do is enable your COM port (5 or 8). After you have enabled this COM port, open up Microsoft ActiveSync and assign the same COM port.

  File-->Connection Settings-->Allow connections to one of the following: (this where you select COM 5 or COM 8, depending on your selection)

After this is done, the rest is done through your MDA. If you go to your COMM Manager, and select "Sync" there is an option in the menu to sync using Bluetooth. When you attempt to do this, the MDA will tell you there isn't a device configured to do this, and would you like to do it now. Say yes and follow the steps. It will search for your laptop and find it. Select it, press next, and it should ask you for a password. You have to enter the password on the MDA (whatever you want) and then enter that same password on your laptop. Once you've done that, the two are paired.

The next screen tells you what services are available. If you get the service "Serial Port," something went wrong. Delete the laptop from your MDA and select the other COM port and try again.

I'm sorry you're having so many problems. I suffered the same fate for many weeks. I hope you get it up and running. When you said you were having problems, I made a special trip into to work to see if my MDA would sync without yet another configuration change. It authenticated when I asked it to sync and everything is fine.

I think the key point here is that you need to most of the configuration work on the MDA. For the Belkin adapter, all you need to do is turn on one of the serial ports. For Active Sync, you just need to associate that port in the connections. The rest of the configuration will occur on the MDA.

Hope this helps!