Your Ethernet LAN adapter is 100Mbps, no such thing as a 100Mbps wireless adapter, or a gigabit one for that matter.
What is the make\ model of the wireless adapter in the PC? You should find it in the same section of Windows device manager as the LAN adapter. However,the wired speeds do suggest that there is a problem with cable\pc, it is a bit odd you are getting the same speeds wired and wireless. Did you disable the wireless when testing wired?
That is a 2 x 2 dual band wireless adapter, with maximum LINK speeds of 300 Mbps on the 2.4 GHz band and 866 Mbps on the 5GHz band using wireless AC. Even if you could use both bands at the same time, it will not get even close to 1Gbps real speeds.
Ahh.. ok griffin ta. He wasn't happy with it for gaming on the PC and so bought himself some Solwise powerlines, that have always been rock steady and he has never complained since. I think the main reason though was he was located as far from my Airport Extreme as he could be in our house !
-------------------- John --------------------
My services: HD TV on VIP (+ Sky Sports & Movies & BT sport), x3 V6 boxes (1 wired 2 WiFi,) SH2 in modem mode with Airport Extreme Router. On VIVID200, Talk Anytime Phone, x2 Mobile SIM only iPhones.