If you have Windows, the included "Paint" program can also be used to downsize a photo to an avatar-friendly size:

1. Click Start, Programs, Accessories, Paint
2. On the File menu, click Open and open your photo
3. On the Image menu, click "Stretch/Skew"
4. Under stretch enter a small number. For a 1.3 megapixel photo (1280 across), try 9% and 9%. Always match the two percentage numbers.
5. Check the dimenions: On the Image menu, click Attributes. You want 120 pixels wide (or less)
5. Once it is the right dimensions, save as JPEG:
a. On the File menu, click Save As
b. Change the "Save as type" list to JPEG
c. Type in a new name and click OK

Also see: Photos - Frequently Asked Questions in the Tech Section.