A quick, easy and free program you can resize pictures with can be found here: www.irfanview.com
If you're interested in animating your avatar or signature pictures, try "Animake": http://www.rms.to/animake.html

I already have Irfanview and its very good. :)

Two things I should mention about "Animake" - the "proper" settings (under properties) for animated photos/avatars are between 3,000 and 6,000 ms, and you have to type in ".gif" after the file name if you want to use "Save as". Those two points aren't made in the instructions.

You can get a free, "starter" version of Adobe's Photoshop album here:
http://www.adobe.com/products/photoshopalbum/starter.html