SetSpriteSize: SetSpriteSize ( mySprite , sizeX , sizeZ ) -- passing -1 as one of the params ensure the sprite retains its aspect ratio
SetSpriteSize to (my_sprite,-1,-1)
Only one -1 is needed, the other number would control the percentage of the size of the sprite, while the -1 in the other place would retain the aspect ratio of the sprite.
I would have the sprite made large, for the highest resolution expected, then scaling down will always give good results for you. Scaling up usually produces artifacts.
Intel(R) Core(TM)2 Quad CPU Q6600 @ 2.40GHz, 2400 Mhz, 4 Core(s), 4 Logical Processor(s), 8gb RAM, Nvidia gtx660, Windows 7 Pro 64bit, Screen resolution 1680 x 1050.