You mean the enclosure of a PC case to punch the holes in? That won't work, because the composition includes plastics in addition to metals.
Also there are punching machines which can be programmed to punch holes in a certain pattern (google: "TRUMPF"), but these are designed for long slabs of sheet metal and are expensive. Are you sure a hammer can make the small holes regularly sized?
My old PC has a metal only top lid.Also there are punching machines which can be programmed to punch holes in a certain pattern (google: "TRUMPF"), but these are designed for long slabs of sheet metal and are expensive. Are you sure a hammer can make the small holes regularly sized?
Programmable machines are a tad too expensive to burn after using them
The size of the holes doesn't really matter, but since the force required increases with the square of the diameter, I expect them to be quite similar. Or get an automatic center punch.