Got a similar problem with the Toyota Previa, and was looking around at some products
one of the cylinders is letting water in, so is misfiring on start, and quite a bit of smoke (unless I drive it every day) but runs ok when running and warm
only paid 950 for it, and its 500 for head gasket replacement, I know they mentioned a product over on the Shogun forums that is supposed to be pretty good but the name eludes me for the moment (it is from the states too I believe)
Mine is losing about 3 pints of water for 5-10 mile trips from cold