Adamus - 10:44 am on Feb 2, 2010 (gmt 0)
I recently came upon a similar issue as I noticed a link reported in Google Webmaster Tools pointing to my corporate website, from a site I didn't actually have a link on. But a form on that site uses a script hosted on my site, so it does look like Google sees those form action URLs and might even attach some value to them.
Seems logical to me in a way - in the crawling & indexation process the Google spider parses the full code and extracts all URLs.
I'm not sure if nofollowing them will help though. PageRank sculpting through nofollow has been hotly debated for a while now with compelling arguments on both sides of the fence. Personally I'm not a firm believer in PR sculpting with nofollow, but I love to be proven wrong. :)