The case looks really old, also the NIC let me imagine that is a very old build.
To make sure the GPU will fit, just measure this distance:
http://www.antec.com/images/product_detail/One/Big/03.jpg it must be at least 5.7" (15cm)
The GPU will also use two slots, so you have to make sure it will not interfere with the NIC when installed in the pci-e slot