Here's the formula that Party Poker uses for its tournament leader board:

15 * ( sqrt ( sqrt ( buy-in amount)) * (number of players – 6) / rank in tournament)

It’s pretty easy to set up on a spreadsheet. Here are some examples of results:

25 players, $10 buy-in, 5th place finish = 101.36 points
25 players, $10 buy-in, 1st place finish = 506.81 points
25 players, $10 buy-in, 20th place finish = 25.34 points
50 players, $10 buy-in, 5th place finish = 234.73 points

In a 25-player $10 buy-in tournament, these would be the points for the top-10 finishers:

1 - 506.80
2 - 253.40
3 - 168.93
4 - 126.70
5 - 101.36
6 - 84.46
7 - 72.40
8 - 63.35
9 - 56.31
10 - 50.68

It looks complicated, but once you have the spreadsheet set up, it's a snap (I'd even volunteer to maintain it).