I agree you could just throw in a PCI NIC and a good option if stick with one listed such as various Broadcom's. Either way I would also check the processor compatibility via the link I posted just in case before you spend any money. If you don't have Workstation then that's a cost too as well as I've seen where Workstation when creating Hosts doesn't work properly due to CPU. Doesn't hurt to play and try stuff if you have spare parts though. Good Luck.
Regards, CSSMP