Does avast offer a free all-in-one security suite siimilar to MSE,
Avast is better than MSE.
Avast have a Web Shield MSE don't
Avast Blocks Malicious Downloads MSE don't
I think avast is much MUCH better than MSE

and why do these two programs conflict?
Two Antivirus programs running in the same PC at the same time Will cause conflict.
For example:
-One will detect the another like a virus and viceversa
-Slowdowns
-Possibly Blue Screens of death...
So i don't recommend you Have both installed (Avast and MSE)
you have any doubts?