I know this might sound simple/stupid to some, but I'm not sure if Midknight has tried this. You should be able to leave the speed setting alone (115 IIRC). Then only use 1 port on your laptop and remember which one it is (for example, only use the bottom port on the left side). If you're changing which USB port you're using it's obviously going to change the COM port. I didn't bother going into device manager to figure out which USB port was tied to which COM port, so I just kept trying to register DHP on different ports until I got to the right one (usually 3 or 4, depending on your setup).
Post up some pictures of the adapter you're using so we can help you out more.
http://www.tripplite.com/high-speed-...yspan~USA19HS/
This ^ is the preferred adapter for pretty much everyone.