As you may know the Nintendo WiFi adapter isn't supported on anything except Windows XP. Well I got it working on Vista and it's easy.
 
Step 1: Plug the adapter into the Vista PC.
 
Step 2: Put the CD that came with the WiFi adapter into you PC's DVD drive.
 
Step 3: Select "Computer" from the Vista start menu and right click on "WFCReg103" CD and select "explore"
 
Step 4: Open the folder NintendoWFCreg and find the application "Setup.exe" in that folder
 
Step 5: Right click on the "Setup.exe" file and select "Properties"
 
Step 6: Goto the "Compatibility" tab, tick the "Run this program in compatibility for" check box and select "Windows XP Service Pack 2"
 
Step 7: Click "OK" then run the Setup.exe program.
 
Step 8: The install will run as normal till you receive a warning that the drivers are not signed, ignore this warning and continue with the install as normal.
 
Then you just need to setup the Nintendo Wii and DS as normal and everything is good.