The error there is that you shouldn't use the x but the comma. I have other suggestions though:
1) Don't use directshowsource, but ffvideosource. Look around in the section for more info about it.
2) The converttoyv12() is useless since your input is already yv12.
3) That filename tells me way more than enough to know that your input is progressive already. You do NOT want to use tfm and tdecimate.
4) Don't use lanczosresize, use spline36resize instead. Just for the sake of clarity: spline36resize(1280,720)
5) Why assumefps(24)? Some particular reason to edit at that instead of 23.976? But oh well, that's a non-issue, really, you're actually free on this.
6) MOST IMPORTANT OF ALL, DON'T USE VDUBMOD! Use the latest stable vdub instead! virtualdub.org is the homepage, moving from there is easy, and you'll have to choose between 1.9.11 stable and 1.10.0 experimental. I personally use 1.10.0, but feel free to use 1.9.11 if you want to be safer.
7) If the reason for using vdubmod was the avs editor, avspmod is a much better replacement:
http://forum.doom9.org/showthread.php?t=153248