I'm a little surprised an ethernet card is causing issues, I've had this and my previous three or four DAW PCs connected to the router by cable (right back into the days of resistor terminated co-ax network cables) without issues. Still, that's PCs for you, no two are ever quite the same.
Wireless on the other hand can be a nightmare as the combination of how Windows handles networking and multi-tasking and the drivers themselves very often cause excessive PCI bus delayed procedure call latency. Which in turn means unless the ASIO buffer is increased we get crackles and dropouts.
I do have a computer which, though less powerful than the one in my sig can run wireless networking without a glitch at a 64 sample buffer with round-trip audio latency of around 5ms. Unfortunately that computer can't run Sonar.
Wireless networking and the issues that come with it really is something the card/chip builders and Microsoft should sort out, but as the dpc latency is only noticable to people who use DAWs, edit big video files and similar processes that require very close to real time operation I guess they don't regard it as a priority.