I'd love to view your stuff, but you are doing everything for Windows only. AVI's suck for quality and do not allow others but Windows users to view your stuff. You should use Quicktime... it is far superior and you will be pleasently surprised at the level of your control.

In answer to your Motion Blur question... Are you compositing in a seperate program? If not, you really should.

You should render your TRex with no background for the full duration and then composite him on top of you film clip or image file. Also watch you lighting sources to make it look more like he is actually in the scene.

I tend to shy away from motion blur in my Maya renders as I get far better control and sharper imagery if I add the blurs in Combustion.

Hope this helps.