At http://www.intel.com/cd/channel/reseller/asmo-na/eng/53211.htm Intel gives all the specs for correctly integrating CPUs with Prescott core (Pentium 4 and Celeron D). Let's talk about the case requirements.
Regular cases usually keep the temperature inside the PC between 104º F and 113º F (40º C and 45º C) with an ambient temperature of 95º F (35º C). In the Prescott specs, Intel asks to keep the temperature inside the case only five degrees Fahrenheit (three degrees Celsius) above the ambient temperature, which must be up to 95º F (35º C).
So, the main casing requirement is to keep the temperature inside the PC below 100º C (38º C). The case may not follow the design specs from Intel, but it must be capable of keeping the PC inner temperature below 100º C (38º C).
In order to achieve the required temperatures, Intel released its Chassis Air Guide Design 1.0, which uses a case with a 60 mm duct on one of its side, adjustable to correctly fit the processor, pulling fresh air from outside the case.
Figure 1: Correct case airflow, according to Intel.
Figure 2: Correct distance between the air duct and the CPU cooler.
In order to make the air enter the duct and cool down the CPU, it is necessary to have an 80 mm fan installed on the back of the case, pulling hot air from inside the case to the outside. The duct must be installed between 1/2" and 13/16" (12 and 20 mm) away from the CPU cooler to work (see Figure 2).
Figure 3: 80 mm fan for removing the hot air from inside the computer.
These recommendations are for low cost PCs based on the Celeron D processors.
For more advanced systems using the Pentium 4 CPU and more powerfull video cards, Intel noticed that the above specifications were not enough, so they released the Chassis Air Guide Design 1.1, which increases the side duct to 80 mm, the rear fan to 92 mm and also added a side window on the case above the motherboard slots, in order to cool down the system daughterboards (see Figure 4).
Figure 5: Chassis Design Guide version 1.1 adds a side window and increases the side duct to 80 mm.