YO people all youve gotta do is download a free program (usually the best software is free) like
irfanview.
then install it and tell it to associate with 'images only'. then open your .jpg or .bmp or .gif or .tiff or whatever format your avatar may be in and then select (from the menu at the top) Image then Resize. (or press CTRL-R instead)
Set your size for datto1200.com compliance and then choose File and Save As.
change the file type to JPG and then you can move the Quality meter down to its lowest possible point, while retaining an ok looking avatar. you can save it a few times with different quality settings (and different filenames) and find the best looking one to use.
here's a direct link to the irfanview installerhope this helps out