All decarboxylation means is drying and curing. That's why it is most noticeable with fresh/wet weed. Decarboxylation occurs naturally as you dry your weed. You can heat it up if you want to decarboxylate faster.

This quote is from Ed Rosenthal and can be found here:
Decarboxylation

Marijuana produces THCA, an acid with the carboxylic group (COOH) attached. In its acid form, THC is not very active. It is only when the carboxyl group is removed that THC becomes psychoactive. When marijuana is smoked, the THC behind the hot spot is vaporized as the hot air from the burn is drawn through the joint or pipe bowl to the unburned material. The liquid THC and other cannabinoids have a boiling point of between 180-200° C (355-392° F). Before they turn gaseous, at around 106° C (220° F), the carboxyl group is released from the molecule as carbon dioxide and water vapor.

You will be extracting the THC using low heat in the commercially made Coldfinger Extractor. (They have a very interesting online catalog at *edited out commercial site*). The THC will not reach a temperature in which decarboxylation takes place. However, if you plan to vaporize or smoke the extract decarboxylation will take place as the oil is used.

However, it is easy to make sure all the THC is decarboxylated and is at full strength before it is extracted. Although decarboxylation takes place rapidly at 106° C, it proceeds at a more gradual pace by placing the cannabis in a room with low relative humidity and room temperature. As the temperature rises, the rate of decarboxylation increases.

Cannabis can also be placed in a food dehydrator to remove the carboxyl group. Although the heat in the food dehydrator doesn't rise to 106° C, the temperature is warm enough to promote drying and the release of the water and CO2. When the marijuana is crispy and brittle you can be assured that the carboxyl group has been removed from the cannabinoids and they are ready for extraction or removal from the plant material.
Here's some more:
Frequently asked questions

# Franjo Grotenhermen
In the plant the cannabinoids exist mainly in their carboxylic forms as cannabinoid acids. However, the phenolic form of THC is responsible for the psychotropic and the most medicinal effects. Decarboxylation (separation of CO2) to the phenolic form occurs readily over time, upon heating or under alkaline conditions.
The ratio of THC acids (THCA) to phenolic THC has been reported to range between 2:1 (Africa) and >20:1 (Switzerland) in leaves and flowers of Cannabis sativa. In plants grown in Middle Europe (United Kingdom) from Moroccan, Sri Lankan and Zambian seed stocks the THCA/THC ratio was 17:1 compared with 2:1 in the plants from the original areas (Africa, Asia). In hashish (cannabis resin) the THCA/THC ratio was reported to range between 6.1:1 and 0.5:1, the latter in hashish from India. Thus, the percentage of phenolic THC of all THC in cannabis products varied between less than 5% in cannabis leaves grown in Switzerland up to 65% in hashish from India.
Cannabis products with a high content of phenolic THC (e.g. hashish) may be very potent without heating, but usually the potency of cannabis products is considerably increased with heating (smoking, cooking).
Modified according to: Grotenhermen F. Pharmacokinetics and pharmacodynamics of cannabinoids. Clinical Pharmacokinetics 2001, in press.