http://ytmnd.webspacemania.com/flvv/ online converter watermarker and both static and animated gif screenshots .try it, its free and requires no downloads , just upload your video to your own server enter the url and cablam
( it converts it to flv , but you dont have to use the flv you can just save the screenshots )
alternative you can use
http://flv4free.com my other flv converter you can specify the screenshot time you want like 5 seconds or whatever