Is it possible to burn from within PowerEncoder MPEG-4?

No, this is not possible yet.

PowerEncoder MPEG-4 AVC Edition 1.0 does not have its own burning engine and therefore relies on other programs to burn its files. At the development stage a burning engine for MPEG-4 files was not deemed necessary because MPEG-4 files are meant for streaming and because the Blu-Ray and HD-DVD discs, which can hold 27~54GB, soon will be available.

However, since many users are requesting this feature, it will be available in PowerDirector 5.0 around October, 2005.