FFDSHOW is not a encoder...its a decoder (well technically its a directshow filter..but we'll not get into that

). Also since you no doubt got it from the sourceforge page, which unfortunately hasn't been updated in a while...but the program is still under development. The current version does work with new features in Xvid 1.0 that the older version on the page doesn't have. for the latest built versions visit,
http://athos.leffe.dnsalias.com/
Virtual dub however is a front end to the ability to encode
http://www.virtualdub.org/ is its home page..one that should do what you want, you can do a lot with it...but its no avisynth.
Avisynth, since i'm on the topic is basically known as the program to use for the best perfect video you could ever produce. You have practically a endless ammount of things you can do with it. However its a manual method of doing a video (not something you just jump into). I'll see if i have a copy of a file you have to create to use avisynth but your best bet is with virtual dub for what you want to do. Just a little history lesson

about quality video production.
Absolutely do 2 pass encodes....if you do anything else I shall come and bonk you over the head of degrading the video quality, and making the video larger then it has to be. (2 pass basically does a first pass to see every frame of a video and then decides what can be tossed lost etc to make it to the size you want the video to be. Very handy to have, and it'll come within a few meg of the actual size you want the file)
Couple of questions..1) are you wanting to have it playable on set-top dvd players...if so you'll have to convert them to dvd quality video ie MPEG-2 standards. If you just want to burn it to disk and use it on computers..I'd suggest Xvid (go here for the best one to use
http://www.roeder.goe.net/~koepi/xvid.shtml ) or Matroska due to size and other issues. Course on any computer you want to play it on you have to have the same decoder as what you encoded it as.
And please please avoid using WMP encoder....they claim its wonderful but...blargh!
Also please not that Divx etc is a encoder/decoder its not a plug in for vdub. (all encoder/decoders have .dll's residing within the windows system32 directory iirc) Plug in's for vdub do such things as adjusting levels, blending video so it appears a bit less grainy, increasing the graininess of a video when its been blended too much. Changing the range of colors in a video if for example in the taping of it, they've been washed out.