Hi, There is a barcode sticker on the motherboard (near one end of the RAM slots). The last 4 digits on the sticker stand for the BIOS version.
Then check here http://support.asus.com/cpusupport/list.aspx?SLanguage=en&p=1&m=P8P67-M%20PRO&hashedid=iT2FJPCMOGBHClu4
what CPUs are supported.
As an option, since the BIOS chip is on socket, you can order a BIOS chip (ASUS eStore in US or ebay) flashed with the latest BIOS version and replace the board's one.
It's not difficult: http://www.youtube.com/watch?v=pLEQoWRq41k