Yes, there is. (this should work). Open member.php and find
$db->query("INSERT INTO ".TABLE_PREFIX."users (uid,username,password,email,usergroup,regdate,lastactive,lastvisit,website,icq,aim,yahoo,msn,birthday,allownotices,hideemail,emailnotify,invisible,style,timezone,threadmode,receivepms,pmpopup,daysprune,regip,showcodebuttons $queryad $queryad2 $queryad3) VALUES (NULL,'$username','$md5password','$email','$usergroup','$timenow','$timenow','$timenow','$website','$icq','$aim','$yahoo','$msn','$bday','$allownotices','$hideemail','$emailnotify','$invisible','$style','$timezoneoffset','$threadmode','$receivepms','$pmpopup','$daysprune','$ipaddress','1' $queryadd $queryadd2 $queryadd3)");
$uid = $db->insert_id();
and replace with
$db->query("INSERT INTO ".TABLE_PREFIX."users (uid,username,password,email,[b]avatar,[/b]usergroup,regdate,lastactive,lastvisit,website,icq,aim,yahoo,msn,birthday,allownotices,hideemail,emailnotify,invisible,style,timezone,threadmode,receivepms,pmpopup,daysprune,regip,showcodebuttons $queryad $queryad2 $queryad3) VALUES (NULL,'$username','$md5password','$email',[b]'images/avatars/clear_avatar.gif',[/b]'$usergroup','$timenow','$timenow','$timenow','$website','$icq','$aim','$yahoo','$msn','$bday','$allownotices','$hideemail','$emailnotify','$invisible','$style','$timezoneoffset','$threadmode','$receivepms','$pmpopup','$daysprune','$ipaddress','1' $queryadd $queryadd2 $queryadd3)");
$uid = $db->insert_id();
(
Bold bits are the added bits)
Change
images/avatars/clear_avatar.gif to whatever avatar you want.