Jay, PCI-e/AGP is just the bus/slot it plugs into. What is the computer/motherboard you’re running? If you don’t know, run a program called belarc advisor (it’ll give you a run down of all installed hardware/software) and let me know what it says.
Either way, either one will do fine (agp or pci-e)… only real difference is the AGP needs a seperate power source (aka, plug the card into a molex connector from the power supply, much like you would a CD-Rom drive)… PCI-e doesnt need it as the buss supplies enough juice to run it stand alone.
If it’s for cad work, you wont need all the fancy shader model 3.0 features so with that said… what is your price range? that x1300 will do you good IMO. I just got my 7800gs and it runs 3dsmax/solidworks great, but it’s more of a gaming card so… I guess it’s just an added perk