I have the Temma 2M (different serial port), but I had no problem the three times I have tested it with PHD - just set the mount to "On-camera", connected to CCD Labs Q-Guide camera and away it goes.
Of course, I am waiting for an SX M8, so I have not really taken any pics that need autoguiding, but PHD went through its routine -North, South, West and East for 10 iterations each direction and the graph looked reasonably (but not perfectly) flat.
In the old days of 28.8 modems, I always had trouble with telephone jacks with laptops - being plugged in and out took its toll I suppose - it isn't that?
Either that or it could be a win7 issue. Tom from the QHY forums recommends using it through the ASCOM platform
http://qhyccd.com/ccdbbs/index.php?P...1&topic=1924.0