you would set that in your admin control panel

"Profile Settings" and the "Avatars" tab

make sure the path ( disk based location ) is writeable and that the URL ( web based location ) are consistent.

for Mindraven, they use WHM / CPanel, so the path would be something like:

/home/yourlogin/public_html/yourforum/images/avatars

and the url would be:

http://yourforum/images/avatars

2c