Iraq has had lots of chemical and biological weapons for the least two decades. During the 1980s, Iraq used hundreds of tons of mustard and nerve gas against Iranian troops. Most of it was mustard gas, which blisters the skin and lungs (if inhaled) and can kill, but it usually just crippled. The Iraqis produced three types of nerve gas; Sarin (easy to make, but breaks down quickly, sometimes within minutes, when in the open), Tabun (like Sarin, but harder to make and lasts longer when used) and GF (very hard to make, but lasts for days on the ground and vegetation.) Nerve gas causes the nervous system to fail, often resulting of death when the lungs stop breathing.

The Iraqis had trouble making Sarin that would last even when stored inside shells or spray tanks. The stuff would often degrade to uselessness within a few weeks. In 1989, the Iraqis destroyed over 40 tons of Sarin that had decomposed and become very weak (but still deadly if you took a bath in it)

During the 1990s, Iraq admitted to UN Weapons Inspectors that it had manufactured 2,245 gallons of Anthrax spores, 5,125 gallons of Botulinum toxin, 581 gallons of Aflatoxin, 2.7 gallons of Ricin, and 90 gallons of Chlostridium perfingens. The UN inspectors believe, based on the manufacturing facilities they saw, that Iraq actually produced three to four times as much as they declared. 

Same with poison gas. The Iraqis only admitted to having four tons of VX, 150 tons of Sarin and 600 tons of Mustard. 

Iraq said it destroyed, but could not confirm it, 16 Al Hussein missile warheads filled with botulinum toxin, five with Anthrax and four with Aflatoxin. There were also a hundred R-400 aerial bombs filled with botulinum toxin, 50 with Anthrax and seven with Aflatoxin.

Also unaccounted for were four aerosol spray tanks for aircraft that could be used to deliver biological or chemical weapons. Finally, there was nearly four tons of growth media for biological weapons unaccounted for.

During the 1990s, UN inspectors did confirm the destruction of;

38,000 chemical weapons

- 120,000 gallons of chemical weapons agents (83% mustard and 17% nerve agents)

- 450,000 gallons of 45 different precursor chemicals - the raw materials for chemical weapons

- 48 operational missiles

- 30 special missile warheads for chemical and biological weapons, filled with agents including the nerve agent Sarin

- chemical and biological weapons production equipment.

Current inspectors will almost certainly find some chemical and biological weapons the Iraqis "disposed of" by simply burying them. Iraq never built proper disposal plants for the stuff. The smoking gun, of course, would be finding shells, rockets and bombs full of Mustard, nerve gas or biological weapons and ready to be used. This may not happen. Saddam may have decided to destroy, or bury, all his ready to use chemical and biological weapons, mainly because they were too prone to corrode and leak. This was seen in the early 1990s when UN weapons inspectors saw stuff that had been manufactured in the late 1980s.  Iraq has lots of desolate deserts where stuff can be buried and abandoned. These sites won't be found until American investigators get to Iraqis involved in these burial operations and convince them to talk. 

What Saddam did want to hide were his weapons scientists and their labs. Those people, and some of their labs, are probably out there, and will probably be found eventually.