At 3.2 GHz, P4's and PD's were getting to the end of their capabilities. You can successfully OC them, but it takes a lot to push them much further than a puny 5%. Air cooling is tricky since those CPU's are already really hot, but it can be done. Water cooling is by far preferred since you have a chance to push them into the 4 GHz range, which is needed to get a measurable performance gain out of NetBurst!
In the end, however, your mileage may vary and we officially do not endorse OC'ing as a means to getting more performance out of a system. There's always the chance that you could fry one or more of your components, void warranties, lose data, blow fuses, etc etc. Conversely, there's NOT always a chance that you will gain more performance. That's why OC'ing is still more of an art than a science. It gets easier all the time, but there are still no guarantees whatsoever.
Your second question about a supporting mobo for your P4 begs additional questions from us. If you don't already have a mobo for an old P4 CPU, why bother using it at all?? P4's are far out-stripped by the latest Intel and AMD CPU's in every benchmark. Why build a system around an old CPU when you can build a system around a new CPU?