wrong forum but no doubt it'll get moved so I'll carry on :P I've seen a lot of posts about ratings mods and/or karma mods although I'm not certain whether anything's ever been done, try searching here and on snitzbitz. if there's not it wouldn't be desperately hard to implement I wouldn't have thought.... a rough and quick way would be similar to what Proboards now have on their forums - just add a karma column into the members table then place a link next to the post to increase karma or decrease which can either link to a seperate page to update the db or simply add an extra querystring to topic.asp, and if that's present update the database accordingly with current karma value +/- 1.
As for the avatar a search would immediately throw back: http://forum.snitz.com/forum/topic.asp?TOPIC_ID=60156&SearchTerms=user,upload,avatar as i just proved <