Windows 8 will not install on MOST Pentium 4, with the exception of a few models, like 630, 631, 940 which support NX, or you will get an error at the beginning of your install. You need to look up the features for your S-spec. Also make sure your motherboard BIOS will support the feature(s).
unreal9400 is right.
The quoted comment by Hopachi/vrosa refers to Consumer Preview, that's what CP stands for. You used to be able to install that version on any Pentium 4 and even Pentium 3, but since the end of January CP can no longer be activated.
SuperGamerBoy's suggestion is the easiest way to determine compatibility. It deserves a "Best Answer" post.