I use the IOGEAR GUC232A USB to DB9 serial adapter. I haven't used it for ProntEdit yet, but it works great for Meridian, Crestron, and Hyperterminal PC to PC transfers.

This piece will let you assign it to any COM port. I notice that sometimes, with Windows applications, it will hang and needs to be reset, but I haven't been not able to do anything that I could do with my other computer.

I first tried the BAFO adapter and that didn't work for me at all.