AGP 8x refers to the data rate transfer speed of the interface between the board in the AGP slot and the motherboard. basically, AGP 8x is faster than AGP 4x.
anyways, i'd recommend checking out the GeForce 6600 GT lineup. the reason being is that it's the fastest and the most up to date graphics board available for the AGP interface. it might be more than $80 in some places, but IMHO, its worth the extra $10-20.
just my two pennies.
See the struggle of the faithless lot as they negate their time
How low to sink to the depths of their frame of mind