bstrides, The system has 4 pic slots on the motherboard. The reason the high end graphics card you bought would not fit is because it may have been a pci-xpress card. There are no Pci-xpress cards on the motherboard. You should not worry about the network card  bottleneck. Just purchase a PCI 10/100 network card and you should be fine.
Hi there, I have an old Dell Dimension 2200 desktop running Windows XP which currently connects to my router via a USB wireless adapter.  For a couple of reasons I want to replace the adapter with a networking cable (the computer and router are next to each other) but am not sure how to best go about this. Looking at the back of the tower I can't see any networking sockets except for the 56K modem card which came with the computer, so presumably I need to buy a network adapter and get hold of the relevant driver? Is that right and if so where might I find these things? Thanks, B    System specs:        
Connecting Dell Dimension 2200 desktop to router