The problem with ASF (Advanced Streaming Format?) is the audio... Its really simple: download dbPoweramp at http://admin.dbpoweramp.com/dmc.htm
you also need the WMA Codec here http://admin.dbpoweramp.com/codec-central.htm#Windows Media Audio (WMA)
use this proggy to convert the audio of your ASF file to wave
once you seperate the audio/video use you favorite encoding proggy to combine and encode to what you want..
I gotta tell you though, after doing this several times, you really can't beat the small size of asf file to mpg, unless you are making a VCD