PCI- Express

Hi There - I have just purchased a small server (Dell Poweredge T110), which has only come with one on board Ethernet controller installed. I am going to buy a new pci-e network adapter to install but I have been told that I cannot just get any pci-e card that it needs to be compatible with my server, is this correct? I can see several 1x, 2x, 4x 8x pci-e slots inside and its a tower so Im assuming that no special requirements are necessary that any standard pci-e network adapter would fit!! As far as I am aware it doesnt matter weather its a computer or tower server at least? I could understand if it was a rack server but otherwise its the same I think???

Please can someone help

Thanks All