Easy!
Open file xoopsroot/header.php in an editor and look for this code (2 occurences):
'xoops_isadmin' => $xoopsUserIsAdmin
Paste directly after this code (for both occurences):
, 'xoops_avatar' => $xoopsUser->getVar('user_avatar')
The user-avatar would be called like this in a template or in one of the theme-files:
<img src="<{$xoops_upload_url}>/<{$xoops_avatar}>" />
Doesn' work with 2.2.3!!
Please! i need this hack corrected, so I can use it in XOOPS 2.2.3!!!