this was a problem for me too. i have two versions maya 6 and maya 8. to get cad drawings into maya, i did;

first way
you save the cad drawing as an autocad 2000 file. i was unable to open the 2007 version in maya 6.
then proceed to maya 6 and then import the file into maya (make sure you have the dwg plug in activated).
from there you save the file and then open it in maya 8

second way ( recently found out)
for you guys with maya 8 go to this link

https://usa.autodesk.com/adsk/servlet...&siteID=123112

and get the DirectConnect Products for Maya this allows you to import the cad drawing directly into maya8 once the new plug has been installed.