What Admiral said is a good point. If you want to do this painlessly get an exact replacement. This may not be possible if the PC was a brand name (Dell, Gateway, HP/Compaq/eMachines). They discontinue boards pretty often. Even the OTC vendors may not still have a board after 2 years.
We need lots more info on the MB and CPU-
-Socket type? LGA 775, socket 479, etc
-Is it a 533 or 800 mHz FSB on the CPU?
-Does he need built in video on the MB?
-Any special sound requirements?
-Is the power supply ATX1.0, ATX 2V12, ATX 2.2 etc. The power suplly to MB connector options are all different.
-Does he need/want SATA HD ports?
-Firewire or just USB 2.0?
-Is it DDR or RAMBUS memory?
-What is the size of the MB? ATX, microATX, special?
BTW - what do mean fried? A major failure could also have damaged the RAM, CPU, HD, Optical. You need to make sure the rest of his parts are good before proceeding with a MB swap. Testing in an old machine is the safest approach. I keep one around for this purpose.
And now the ugly news. If it was a brand name computer there may be restrictions on compatibility.
-His copy of Windows may not boot unless it sees a special Bios flag.
-The power supply may be limited capacity or have special connectors.
-The case may not fit standard ATX type MB's.