Amir 2010a, You can use Global Mapper for convert KML to DWG.
Note:
After export KML from Google Earth,it coordinate system is Geodetic or Geographic.
After import kml to Global Mapper go to Menu Tools / Configure and select Your projection system and datum.
for example in IRAN, Tehran : Projection: UTM / Zone : 39(48 E - 54 E -Northern Hemispher) / Datum: WGS84
Go to menu File / Export / Export Vector Format / DWG.
Good luck.