What I have done in VB is as follows:

I make the VB form have a chooser box where the user can select the COMM port that they want to use. Before displaying the box (at form load time) I have VB run a scan and try to open say the first 100 communications ports. If they fail to open I skip them. If it did open I then close it right away and add its COMM id to the chooser box.

If you run on a slow computer then reduce the number that you try to scan to 50 or 30 or 20. I have found that a scan of 100 on a 900 MHx computer takes only a short time.

Michael Karas

PS...I have also done this in VC++6. Someplace I have a small application that shows the results for the first 100 comm ports. It seems misplaced at the moment but if I can find it I can link it here.
MJK