Downgrading is out of date and is only used now mostly by misinformed people. There is absolutely no reason to downgrade your Wii any more. The newest SM (4.1) has anything and everything 3.2 has plus all the new features from Nintendo.
Check out the guide in my sig.
Edit: And if you read the last few posts of this thread, you'll realize that downgrading is a good way to brick your Wii, too. Don't do it. =)