It largely depends on your network card. If your network card has a TOE (
TCP Offload Engine) and intelligent interrupt management, then you can probably handle the traffic. However, as NICs with this capability are rather expensive (costing more than most people spend on a PC these days), odds are that that you cannot.
The TCP/IP stack in Linux has not remained static over time, and performance has changed. Your specific throughput will also depend on many additional factors - the specific Ethernet card and driver revision, mix of packet lengths in the traffic, tuning options. Any site that gives you an estimate is literally providing a wild-assed guess.
Your best option is to get yourself a good quality 100Mb home router (typically available for about $50). You may want to look into one supported by
OpenWRT so that you have full control over the Linux running in the router.