textures that use odd dimensions get slightly distorted in-game such as:
24, 48, 80, 96, 192 etc. Stick with 'doubling dimensions' eg. 8, 16, 32, 64, 128, 256 etc. try not to use any other dimension for a cleaner texture. And as Capn' P said, wally converts bmp's into 8 bit when you import them, so they will lose a little quality if you made your textures initially in 24 bit or higher.