So can I just solder an AGP slot on this motherboard and

Short for Accelerated Graphics Port, AGP is an advanced port designed for video cards and 3D accelerators Developed by Intel and introduced

AGP and PCI are both bus's BR>BR>AGP is not a buss, it is a Port that sits on the PCI bus, hence the name, Accelerated Graphics Port BR>BR>

agp slot image AGP - Video card AMR - Modem, sound card CNR

agp slot meaning Either it's a PCI or PCIe The only reason that motherboard could have an AGP slot, is if the motherboard is custom built with that function in