This is true. There is likely a single installed card (and maybe an old modem....) plugged into a brown slot that is offset differently than the PCI slots. That is the AGP slot.
If for some reason, your particularly variant only has PCI slots, then you can look here for PCI options:
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100007709%20600007853&IsNodeId=1&bop=And&Order=PRICE&PageSize=20