is it good to bi-wire or bi-amp a sub, i have a subwoofer box that alows this, but is it good to do?
 
Its a Alpine Type R the 2 Ohm one
 
Sub model Alpine SWR-1222D and amp is Alpine MRD-M605
 
Is your amp 1 ohm stable?  
 
 
if it's a single sub, the only way you can wire the sub is in series giving the amp a 4 ohm load.  if you had the dual 4 ohm coil sub, then you could wire it in parallel and give the amp a 2 ohm load.
 
 
how would i do this? and will it be benificial?
 
check my sticky, it should have series and parallel wiring.  and yes it's going to be beneficial for you to wire your sub @ 4 ohm so you don't cook your amp!
 
 
why would i cook my amp, its fully capable to handle a 2 ohm load?
 
Your amp is stable for a 2 ohm load.  Only way you can wire your sub is 4 ohm or 1 ohm.