what is the file name of the gears???because i'm using a original nba live 08 without any mods install and there is no sleeves there at the create player??
Download this and extract the file inside to your sgsm folder to re-enable access to the bicep accessories, which will allow you to assign and remove sleeves in Create/Edit Player.
Not from within the game. You can replace the default textures of the accessories or assign custom accessories to a specific player but that's all done by editing the art files externally.