Yeah .gif is the preferred method of saving charts and screenshots - having said that an increasingly popular alternative is .png which is a newer format, but one that isn't supported in older browsers. It benefits because it has a great colour range (you won't get the graininess like above), and can often be smaller kb size. Mspaint, is pretty awful when it comes to image editing and it doesn't optimise anything - you'll find if you use a program like Macromedia Fireworks or Paint Shop Pro, it will create gifs which don't have the graininess of above.
As for why the image had a white space to the left. MS Paint acts a bit weird when you start taking print screens of different sized windows, and pasting them into the program. If there white space when you're viewing the image in MS Paint, then it's going to still be there when you save it - so I think you'll have to change the size by going to Image -> Atrtibutes and then changing the width/height. Very un-userfriendly - in the long run you'll save a lot of time by using one of the image programs mentioned above - I use Macromedia Fireworks and it's great.