Bridie, sorry to hear you're so frustrated by all of this - I think what happens is some of these article sites put out an RSS feed of their content, just like VAF does. Then you have 'scraper' sites that literally exist to scrape content in as easy a way as possible [either with bots or via RSS or both]. It sounds like that's what's happened here. The good news is that none of the sites seems to have stolen the entire content of your articles which is more often than not the case, so at least you have the consolation that the 'spam' articles are all pointing back to the article site which in turn points to your site and credits you as the author. Sometimes, traffic by proxy is better than no traffic at all. I guess it all depends on how you look at it.
If you're posting articles strictly for the backlinks/
SEO I'd suggest posting the main article on your OWN site/blog and then linking into the article itself from sites like Technorati, VAF, Facebook, Stumble, etc. etc.
In thinking more about it I'd even wonder if this article site doesn't have some of these scraper sites set up themselves, or at least encourages the behavior, to provide more backlinks to their own site.
In any case, there's a quick and easy way to get the content de-indexed by submitting a spam report to Google, but be careful not to accidentally report one of the 'good' sites as spam - no sense in diluting your article's reach at this point.