I've had problems using USB to serial adapters. I went through three adapters before I found one that worked.

I haven't used it in quite a while since I upgraded my remote. I'll dig around and see if I can find it so I can give you the brand/model number.

As far as the serial port goes you might want to test the port. Do a Google search for loopback test.

Also, try this. In Vista go to the Control Panel, Phone & Modem, (you will need to input your area code in one of these steps) click on the Modems tab, select your com port, and click on Properties. Another window will appear, Open the Diagnostics tab, and click on Query modem. You should get some results. If there is a problem with your com port it should reflect a problem in the results.

Good luck!