I'm design some weapons image, in window XP I can design direct from origin image later save in new name and I don't need attention image background when I start game because it auto remove background when I start game
but in window 7 I can not do that, my weapons image show background, I want erase backgrond from my image, but I don't know how
can someone teach me erase image background ?

Well, I highly recommend you to use another software for editing your sprites. MSPaint is really doubtful in therms of spriting and your archives cannot be recognised as a sprite some times. Photoshop and GIMP are very good alternatives to try; i preffer GIMP because for me its more simplier than Photoshop.

Forgive the lack of time in this answer.