Windows Defender (Windows 7) and avast version 8

Do I have to disable Windows Defender in Windows 7 when using avast! free version 8?
They protect both against spyware. Will there be conflicts when both programs are used?

I have both Avast 8 and Windows Defender and they are working together
without any problem.To be honest Windows Defender looks pretty useless.
I actually like to see Windows Defender definitions updates every few days
so I can be sure that there is nothing wrong with Windows Updates.

There should be no issues running the two programs together but as Windows Defender is quite bad in detection levels we usually recommend disabling it since avast already has you covered.

A better program to run now and again just for second opinions would be Malwarebytes.