In Google Webmaster Tools, at the 'Crawl Errors' section. The 'Not Found' errors: are pages that google didn't find and have links to them from your website or are they pages that it found links to from anywhere on the web?
g1smd
8:06 pm on Aug 27, 2007 (gmt 0)
I assume "both".
youfoundjake
9:38 pm on Aug 27, 2007 (gmt 0)
And as g1smd would recommend, if your not sure if its from your site, run Xenu Linkslueth on it to see the results of broken links.