I have the same issue with the Wi-Fi adapter. Basically, just go into
the settings for the wi-fi adapter by going to Control Panel, Network
Connections and right-clicking on the icon for the adapter (it should be
the one with the highest number at the end of its name) and choosing
properties. Confirm that the 'Connect Using' box says 'Nintendo Wi-Fi
USB Connector', then double-click on 'Internet Protocol (TCP/IP)' and
make a note of the IP number and Subnet Mask (these should be 172.16.0.1
and 255.255.0.0). You will need these settings because when you disable
ICS it will clear then back to default. Cancel out of the properties
screens for the wi-fi adapter, then right-click on the icon for your
main connection (it will be the one with the hand icon at the bottom).
Go to the 'Advanced' tab and remove the tick by 'Allow other network
users...'. Click OK to save the settings and you should be ready to go
with WMC. You may have to stop and start the WMC sharing in order for it
to work, but you should be okay.

The only problem with this is that you will have to manually set up ICS
in order to use the wi-fi again, but this is not difficult to do. Just
go back into the properties for your main connection and open the
advanced tab again. Put the tick back into the 'Allow other network
user...' box (if you have more than one network card on your pc, just
choose the wi-fi's connection name from the drop-down box) then click
OK. Now go into the properties for your wi-fi connection's icon and
replace the settings you noted down earlier back into the TCP/IP screen
(ICS will have filled this screen in with different setting
automatically but it is safe to overwrite them).

I hope this works for you. I'd also be interested if anyone has an
easier way of doing this, perhaps using the command line so that I could
just write a couple of batch files to make the changes each time.

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