I have a MacMini circa 2007 that's getting very low transmit rates via wifi, 8-11. I have other devices that are getting full 54, including a MacBook Air. With everything else off, the MacMini doesn't want to seem to go any faster. Since it has been previously connected to ethernet its entire life, I was wondering if there were some settings I can change to speed up the connection. Option-clicking the network icon gives this read out:

PHY Mode: 802.11g Channel: 1 (2.4 Ghz) Security: WPA2 Personal RSSI: -73 Transmit Rate: 11

My new MacBook Air has the following readout:

PHY Mode: 802.11n Channel: 1 (2.4 Ghz) Security: WPA2 Personal RSSI: -66 Transmit Rate: 79

Both have full bars and the wireless router is in the same room to eliminate any obstructions from the equation.

Could the MacMini be connecting at an older protocol, like 802.11b and be reporting erroneously that it is connected at 802.11g? This would explain why I haven't seen a transmit rate above 11. Any further trouble shooting I can try before buying a new USB 802.11n device?

The WiFi router is a DLink DIR-615. I can see other devices, and none, even the other g connected devices, are getting below 30-40 MBit/s. What's going on here?