It's not surprising it shows as unknown. The bios just doesn't have the mobile on its list. What's important is what speed it's running at. The correct stock speed is 12.5x133~1667MHz if it's a barton and 13.5x133~1800MHz if it's a Tbred.
Run cpu-z and check the bus speed, multiplier and core code.
http://www.cpuid.com/cpuz.php
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MSI K7N2 Delta2 LSR|35w XP-M2400 11x214 1.62V|2x512MB OCZ EL 2 2 2 11 2.9V|9600XT|Seasonic 350w
Abit AN7|XP-M2800 10.5x227 1.62V|2x512MB Mushkin XP4000 2 3 2 11 3.2V|9600XT|Seasonic 550w
Asus A7V600|XP-M2600 6-11x202 1.6V|2x512 Crucial PC3200 2.5 3 3 9 2.7V|PCI 32MB gfx|Corsair 450w