Most newer mobos have PCI/AGP lock, so only the fsb and memory are affected. Most mobos have multiple memory timing adjustments too, so even older DDR is no problem.
Most P4's overclock very well with no change to the vcore, especially if you get a good motherboard. There are several really nice mobo's out now (Abit BH7, Asus P4G8X or even Gigabytes SINXP1394 --- Albatron has a board out that seems to do just as well as these others at less cost, but I don't know much about Albatron). Your next concern with overclocking P4's is to get good memory so you don't have to retard the timing and lose alot of the benefit of running a high fsb. Don't count on too high a fsb with a 1.6 or a 1.8. I would go for a 2.4 (C1) or a 2.53 chip if you wanna push high FSB's. I have a relatively older P4 system with an Epox 4G4A+ and a 1.8A and I regularly run it at 2.61ghz (stable) with a displayed vcore of 1.57-1.6v. I can turn that up to 1.7v and hit 2.7ghz (stable), but like running with lower vcore because the added voltage really increases heat.
P.S. Most people going for high fsb's are adding better cooling to the northbridge and some form of cooling for the southbridge because they are directly affected too.
