I think it's a hundred points, then you get a second. How many points depends on the person giving it, and their total post count. Above the individual comments, it should tell you your total number of points.
The first few are 100 each, although eventually they get harder to obtain (as in you need some number greater than 100 to reach the next bar after a certain point.) And as Pheonix points out, different people have different amounts of points they can give you (they can't differentiate themselves -- just if they have a higher rep power, you get more points if they give you rep.)
Is it not possible to see who has given you positive rep? I wasn't even aware that this forum had a reputation system until I spotted a notification saying I'd received some. >_<