xNES was a rapidly developing NES emulator for DOS, Linux, and Macintosh. However, it was discontinued some time ago due to internal differences within the xNES team. I gather that the xNES code later became RockNES on the PC.
 
The demise of xNES led into the creation of the MESS project, a new multi-console (and now multi-computer) emulator. xNES will not be updated again, and I cannot give you help with this program.