I hav mercury via mothrbod for my pc 3 yr old.mothrbod manual says it has 4x AGP slot.i want 2 buy agp card.?

AGP stands for advanced graphics port. The maximum speed AGP uses is 400 megabytes per second transfer rate and this is through the AGP 4x slot. This is the same as PCI but not close to PCI-E slots. PCI-E travels at 400 MB/s minimum for a 1x slot and 8000 MB/s for a 16x slot. PCI-Ex16 also hooks directly to the northbridge controller of the HUB, as does AGP.