The Pentium 4 draws a tremendous amount of power, more than 50W. It therefore requires an ample power supply to keep it well fed and happy. Specifically, you need an ATX12V power supply, preferably 300 Watts. The P4T proves no exception to this rule.
Any processor that draws over 50W is going to make plenty of heat and need plenty of cooling. The Pentium 4 reference design calls for a one-pound copper base heat sink, active cooled with aluminum fins. Because the weight of the heat sink could destroy motherboards during shipment, Intel designed heat sink bracing mechanisms to stop the motherboard from flexing. One pound of pressure is nothing to a motherboard, but mounted inside a system case in a shipping box, being dropped, moved, and pushed around, the G-forces experienced by the heavy heat sink could increase to the point where the motherboard flexes enough to break traces.
The motherboard with its baseboard removed and the clips which hold the heat sink and board in place
Unfortunately, the bracing calls for extra holes in the motherboard tray, which means reference Pentium 4 motherboards are not wholly compatible with pre-ATX 2.03 cases. ASUS' answer to this was to attach a secondary tray, or metal baseboard as they call it, to the back of the P4T. This tray should allow you to fit the P4T in pre-ATX 2.03 cases without any unusual trouble. Normally, we would be worried that this could cause overheating trouble with the motherboard, since half the cooling surface area of the board would be smothered. However, since the i850 chipset and Pentium 4 both use flip-chip packaging, the majority of their heat channels upwards, away from the motherboard, so we do not expect any overheating trouble from this design change.