You don't need "p3 microcodes" to update the bios, because AFAIK, the p3 has no microcode :-".
You need to identify your motherboard manufacturer and model, go to the the manufacturer's website, download the required stuff and CAREFULLY READ THE INSTRUCTIONS.
Since you don't know what you are talking about, I'll advise you to let someone else do that for you, because you can easilly break the motherboard by updating the bios, if you don't do exactly what's required.
BTW, his should be moved to TechTalk.