I got curious and looked this up on the internet and found this. Very interesting stuff.
http://wiki.answers.com/Q/When_did_they_stop_making_silver_nickels
[Improve] Answer
I assume you are referring to the so-called "war nickels" and not half-dimes. From 1866 to 1942 all nickels were made of copper-nickel alloy. Nickel was a strategic metal during WW2, so to reduce its use in coinage the composition of the 5-cent piece was changed in mid-1942 from to an alloy of silver, copper, and manganese. Only about 1/3 of the alloy was silver so technically there has never been a "silver nickel".
Some 1942 nickels were struck in the old composition and some in the silver alloy. From 1943 to 1945 the silver alloy was used for all nickels. Normal composition was resumed at the start of 1946 and continues to today.
The silver alloy coins bear a large mint mark above Monticello's dome, instead of a small mark to the side. The letter "P" was used for Philadelphia issues for the first time on any coin.
When new, the coins looked very similar to their copper-nickel cousins, unlike the zinc-coated steel cents issued in 1943 that were often confused with dimes. However after a small amount of wear the silver and manganese components tarnished severely and the coins turned an unpleasant dark gray.
Silver "War" nickels were produced by the United States from mid-1942* through 1945. The coins were manufactured from 56% copper, 35% silver and 9% manganese. This allowed the saved nickel metal to be shifted to industrial production of miltary supplies during World War II.
"Nickle"
Be careful of this common misspelling. The metal and the coin are NICKEL. A "nickle" is actually a small European bird (!)
Katz