In NBA Live 2005-08, player overalls are calculated based on player value, which is computed by multiplying specific ratings with either 120 or 100, depending on importance.
I rewrote function that calculates player value and overall in NBA Live 06 and got the coefficients for each position.
Sharing the Excel file for calculating overalls below for NBA Live 06.
This will also work for NBA Live 07 and 08.