I agree with Jester2K II that a 3MP camera or higher is a better buy. The reason I suggested 2MP was to keep in your price range, but if you can find a 3MP with a good optical zoom then this will be the better buy. j.
It really comes down to choosing which is more important to you; an optical zoom lens, or higher resolution and sharper pictures. If the choose the latter, then the Canon A300 wins!.
Having looked at independent sample shots taken on both models, (of an identical subject), the 3.2Mpixel of the Canon shows a significantly sharper picture, compared with the 2.1Mpixel of the Nikon 2100.
As I said earlier, personally I would go for the better picture every time.