my wii has never frozen and like Ryano said you have to more specific..like when does it freeze and where does it usually freeze and what happens to the screen? does turn black or just freezes on the original screen.
Check the cables.
Make sure there's plenty of room for it to "breathe".
Try to have WiiConnect24 closed for some days. Many Wii's have actually melt inside because of the heat. Many Graphic Cards and stuff.
If this doesn't help. Someone else will probably have the right answer. If not, you can allways return it and have it repaired/exchanged.
i'm friends with hockeyperson, and his wii will freeze, like when you're playing a game, it'll freeze while loading, while playing. Also, when you click on a channel, it takes a very long time to load, giving the apperance that its frozen for a while.