Don't waste your time with that stuff.
Do this, it works 100% (I did it on 2 PCs both with Vista and XP):
1) Open your connections;
2) Select both the wired lan and wireless wi fi;
3) Create a bridge between both connections.
Done, that's it, just leave the network options on your 360 on automatic.
BTW, if you get an error when you make the bridge stating that you can't do that while sharing internet connection, just disable that.
Trust me, it's as simple as that!