Be aware that Mpeg4 is not one format but a delivery format with several codecs, not all interchageable but mostly so
Although coming from wmv from WMM, If you have any fresh footage you would be better off encoding directly to the mpeg4 file of choice as you are going from one compressed format to yet another
Most currently available NLE software titles are capable of helping you do this, perhaps with better editing to start with
While you may try the above posters suggestion, I'm rather intruiged that he /she is a new member and both posts are linking to aimersoft: I smell