I've had a really hard time finding a decent free GIF animator that isn't bogged down with adware. These days I just import my images into Flash MX for creation of simple animated gifs, but that's kind of overkill for what you need.
http://www.ulead.com/ga/runme.htm
I used Ulead's Gif Animator years back when I had their Photo Impact program installed; I remember it working really good. I don't know if they have zany limits on their free trials, but this might work for you.