It can be difficult to convert proprietary files like this if you want to use the file in autocad because these people often try to stop this to make you use their resources or services for the conversion.
The "*.dwg" is an AutoCad file, but the format is no longer "standard", and different versions exist. Many software packages read and write to "*.dwg", but not consistently.
Greg
__________________
"The more I learn, the more ignorant I realize I am."