Hi Wheelie53,
As far as I'm aware, I don't think this is possible...since there are many low level drivers etc. that are required for avast! to run, and this would not be possible to run in a portable environment...
I know the U3 version was basically that, but I suspect it ran different somehow...
As a portableapps user myself, I know that there are a few posts about this on the PA forums too...
Scott