welding is joint between the two metals with high temp & 
mostly used in the hard metals.

soldering is a two or more metals joined togrther by a 
melting& used in the light metals

Soldering is a process in which two or more metal items are 
joined together by melting and flowing a filler metal into 
the joint, the filler metal having a relatively low melting 
point, it is distinguished from welding by the base metals 
not being melted during the joining process

soldering is carried out for the non-ferrous metals...

welding is used to joint the pair and soldering is used to 
hard the materail

Welding is a process carriedout for joining ferrous  and 
non-ferrous materials which had high melting points, It 
requires high current to produce high temp.to melt base 
material as well as filler/electrod.
In soldering is a joining process which is applicable for 
low meltiong point materials like tin, lead and plastics.

all above answers are technically not correct...
correct answer is in 
  welding: two metal are joined by taking them to reach
their melting point and fused together
  soldering: joining two metal by applying another metal
which is melted and cooled down over the joint..

welding is a process of joining two metals with ferous 
metal at melting temp. 

solering is process of joining two metale with non-ferrous 
metals at less than 429 degrees