GIMP is free and all you do is add (xms) after each layer name, with x being a number. 1000 is the default, if I remember correctly. When you're done, you save the file as filename.gif (filename is whatever filename you want it to be) and set it to be an animation. It'll do the indexing for you if it needs indexing, so I don't know how you'd do that yourself.
In GIMP, you could also just save the whole thing as an animated GIF without the (xms) at the end, and it would just give you the default (1000ms) for your frame speed.