Some motherboards have a variety of settings that permit stable overclocking. Many others lock out some or all of those features, greatly limiting (or eliminating) the ability to overclock.
The easiest way to tell which category your motherboard falls under is to reboot and go into the BIOS. If there are options for setting frequencies (CPU, RAM, PCI, AGP), voltages, and RAM timings, you're in good shape. I'm not familiar with your P4B, so I can't assess how overclockable your mobo is. My advice is to check out your BIOS and carefully read the Intel overclocking guide. Once you do so, feel free to post back with any questions you might have.
That message means there is some form of instability in your system. Run Memtest86 to see if it's a RAM issue. If that software runs through a couple of tests with no errors, it's most likely a CPU issue.
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