That's generally not good. Here's the breakdown on smoke color.
Black Smoke - dirty air filter, restricted air flow, extremely hard acceleration (too much smoke being produced due to uneven air/fuel mix)
Blue Smoke - burning oil. Worn rings, worn turbocharger bearings/seals.
White Smoke - Bad compression, misfiring cylinders, bad injector/injector leakdown, water in fuel, blown head gasket, #8 problem. Its either water in the exhaust, or unburned fuel.
You should only see white smoke when starting (that is actually okay) and then it should disappear. Constantly seeing white smoke is a sign of either bad injectors, bad head gaskets, or a cracked block.
Check this site:
http://www.flashoffroad.com/Diesel/N...ackedBlock.htm
-Steve