ADM, hmm. There wasn't a guide, it was something I worked out myself, except now I can't duplicate it. It might be something that worked with an earlier version of ac3filter and now doesn't or I'm just not remembering what I did.
I'll have to get back to you on that one.

Edit: Nope it just won't work for me now. I wish I could remember what version I was using. Anyway, Doom9's guide is still out of date since ffdshow is able to directly encode ac3 as well.

That is: Original File -> Wave Parser -> ffdshow -> wav dest -> file writer (.ac3)

All the other stuff it talks about is unimportant. You can TRY using ac3filter in place off ffdshow, which is what I was doing before. It might be a problem particular to my PC and the current version or it might not be.