The system if it even boots at all, the BIOS would either incorrectly detect it as a lesser xeon or give you a microcode error such as what I was faced with in the past about 10 years ago.
Here is a link to the microcode error... basicaally the only fix for it is to have a BIOS that is updated for that motherboard to support proper recognition of the CPU that is stuffed into it. ( OR ) get a proper motherboard which is designed with the support and BIOS to support it properly.
http://www.intel.com/support/processors/sb/CS-030181.htmIs there a reason why you must use this older motherboard with a newer CPU which was never really designed for it? The problems you "could" face are many even if it boots vs black screen and bios beep codes, and you will not be able to tap into the full processing speed of the CPU with a slower FSB, since the data on the FSB will be slower than the CPU normally supports if it supports it at all.
I'd really suggest stuffing the correct CPU's supported for that motherboard or get a newer motherboard that supports the CPU you want to run.
However if you want to try this out, you can, and hopefully you can get your money back if it doesnt work as planned.