Converting a freezer into a kegerator to dispense draft beer is quite simple. However most freezers, even when set on the warmest setting, will maintain a temperature below the recommended temperatures for draft beers.
Most breweries recommend a 36-38° F temperature range for their ale & lager type beers, and a 41-42° F temperature range for their stout beers get the best flavor attributes from their products. Temperatures below 36° F will cause CO2 to become trapped in the beer resulting in off taste and a flat looking beer which will only begin to release carbonation when it warms above 38° F.
For freezers, this can be changed by installing a temperature controller (found under kegerator conversion kits) which allows the freezer to maintain a temperature more suitable for draft beer. Temperature controllers simply turn a freezer on or off as necessary to maintain the desired temperature range. Best of all, no wiring is required for most temperature controllers. Just plug the freezer into the outlet cord, put the sensor tube in the area to be controlled, and set the temperature.