To install the laser, place the file downloaded from below into your 
    ...\counter-strike source\cstrike\materials\models\weapons\v_models\silvio.usptac\ 
folder, overwriting the current file in there. 

!!GUN MUST BE DOWNLOADED FIRST, THIS IS ONLY THE LASER ADDON!! 

Note: Deleting the visier.vtf will result in a checkered box appearing on your crosshair. To get rid of the laser, rename the novisier.vtf file in the .rar and replace the current one. 