For those who wonders what this update is about; this is all I have gotten to know about this update, it seems the update is but small modification.
"Thank you for downloading mental ray(r) for maya 1.5. There is now an update that resolves a licensing issue with this software running on the Windows(r), IRIX(r), and Linux(r) operating systems. We invite you to download your free copy of this update, version 1.5.1 (...) "
I do not support Bush! Nor Saddam! Long live UN!