I don't have the exact formula at my hands, but the vdip rating system is inspired by the elo rating, that is used in Chess for example.
The amount of vdip points you get out of the game doesn't depend on your bet, but only on the selected pot type (WTA or PPSC), your final position and the strengths of your opponents. If you win a game against players that are mainly ranked higher than you, you will win much more points compared to a game where you opponents are ranked lower than you. The same applies to draws, survives (if PPSC) and defeats, where you will get a lower loss, if your opponents were stronger.
You can get an idea on how points are calculated when you take a look at the specific calculation tables of some players (you normally find them via the vdip-points-hall-of-fame). Yours is here for example:
http://www.vdiplomacy.com/hof.php?
userID=7441