So you want a .gif instead of a video? What's the file extension of the "slideshow" you made? Video files don't just automatically become .gif(s) on computers; they must originally be saved that way. If you uploaded a .gif to the "video" section of Tinypic, you'll get a video embedded into the forum. If you want to make a .gif, you'll have to get each frame of your slide show and either make a .gif in a program such as Photoshop, or upload the frames to a .gif making site.
Here's a few sites you could use:
gifmaker.me (http://gifmaker.me) - makeagif.com (http://makeagif.com) - www.giflike.com (http://www.giflike.com)
Hopefully that helped.
Sadly enough I am not very sure how to help you with this issue. So I am going to hope that the other replies helped you out. All I can do is wish you good luck on trying to get it solved. :)