If asf is an absolute requirement, pull down version 1.3c form here:
http://www.oldversion.com/program.php?n=virtualdub
Virtualdub used to support asf until Microsoft ‘requested’ they drop it (as of version 1.3d). Also, the fork Virtualdub-MPEG2 clams to support asf files.
But like I said, there isn’t much out there, especially for Windows. Most of the Opensource stuff is focusing on Linux these days. You could pull down VMPlayer and a prerolled linux image and then install one of the Linux video editors I mentioned.