http://support.dell.com/support/edocs/systems/dim4600/en/4600i/sm/specs.htm#1111336
It has AGP 1X, 4X, 8X
So that's good
I agree they normally don't state the voltage of these ports at Dell (very irritating)
AGP technology is old technology, it is possible that the card or slot just doesn't work any more
Or it could be your PowerSupply cannot supply enough voltage to the card
Is it really worth it?