1. There are limitation on what avast processes you can use with winME, they are usually greyed out.
2. The advanced User Interface isn't in the Program Settings (but from the Simple User Interface menu) and is only available with the Pro version.
I don't know if the rootkit module works in winME as the stand alone anti-rootkit tool we beta tested doesn't work in win98, so the same restriction is probably in winME.