What you need to do, Jazz, is Save the file for Web & Devices thingy. A large panel will appear, with lots of options. Just make sure you select the .gif format, and off you go. For size constraints, you should try to obtain the best quality image for least space required.
Signature violates 1.7, please resize:
1.7 - Pictures that exceed 700px width or signatures that exceed 700*250px*3 MB are not allowed on the forum.
Mephistoles