Running Triple Speed Ethernet Design on Cyclone III Development Board

You could try to loopback your transmitted packets right back to your receive interface on your board, without connecting it to a PC. That way you should know if the PHY chip gets your data to transmit correctly.

If you have access to the PHY's MDIO registers, you should be able to configure it in loopback mode to do just that, or an alternative method is to do a wire yourself that connects the rx and tx pairs together.