Hmm... so that was a WiFi connection between your laptop and the Boxee you were referring to that you got 65Mb? If so only half of that is actually throughput.
PCs are tricky. There are all of these theoretical speeds/rates that are not real world. USB, WiFi, Ethernet, PCI boards and it goes on. Bottlenecks and other things are culprits. Plus, good software drivers and so on.
Edit: Curious... do you know if you used mixed cable types (Cat 5, 5e, 6) that the speeds will only work as the slowest cable? I know with WiFi it's speed is only as good as the slowest device. I understand that, say, you have 802.11b enabled and someone is using that then everyone else will run at the 802.11b speed via WiFi. Wondering if the same thing applies to cables.