This was posted once before, but buried in another topic. It's worth a bookmark, IMO.

Wheel weights:
http://www.mysportscar.com/features/wheelweight.htm

Offset and sizing:
http://www.gmpperformance.com/products/wheels_tires/wheels.htm

Tire size calculator:
http://www.miata.net/garage/tirecalc.html

OEM mistu wheel specs:
http://www.newsales.com/wheels/info/Mitsubishi.htm

www.wheelweights.net

for all ur wheel weight needs :)