no mountable systems?

I'm a student trying to download maya 2011 on my macbook running mac os 10.5 (my mac is 3 yrs old and intel based). The program downloads fine but when I click the .dmg i get an error saying "nomountablesystems." Ive been trying for 5 days to correct the problem. Ive tried redownloading, downloading the 2012 version instead of 2011, downloading from another computer onto a flashdrive, re-installing diskimagemounter, using disk utility to try to repair the .dmg, downloading stuffit and trying to open the .dmg, and converting the .dmg to an ISO. Nothing works. I am able to download and mount other .dmg files so I know diskimagemounter isnt the problem. My classmates were able to download and install the program just fine, but for some reason I cant get the dmg to mount for the life of me. Any ideas on what the problem is or other things I can try?