Here is a open-source CableServer replacement for Impact. Currently Parallel III and Alter ByteBlaster are supported, but any 3rd party can be implemented easily and can be used from Impact.
I've tested only Impact 8.2, if anybody has any problem with 7.1, please let me know!
Impact and Xilinx CableServer communication are very pooly written. There is no error recovery at all. If server stops, Impact GUI will crash. To avoid this you must disconnect server from GUI using Output/Cavble disconnect menu.