The Wii Controller thing, I don't know about. I just have a feeling they may be hard to get ahold of. As far as getting them, I can't say how it'll work at any particular Wal*Mart. Again, stores have permission to sell them as soon as they get them in stock - however some will probably hold them back until launch. (Our stores has already had the modular drop with with Wii and PS3 accessories on it.) I would go in (do not call, most associates hate taking such phone calls, espically during this time of year when we're busy enough as it is) and being really nice to whomever is at the counter to see what kind of infomation you can get from them.
Ceric - it depends on your store. Some stores will have people there early in the morning, some won't have people there until late in the evening... Personally, I plan on getting there around 2 in the afternoon (and bringing my DS..)