try a CPU with the similar front side bus, like the T9300 or T9500. Most likely more than 800MHz will not be supported. The T9400 and T9600 do have a 1066MHz FSB.
It really is try and error when it comes to such upgrades on a laptop. Be sure the BIOS is updated to the latest version before replacing the CPU.
Technically it´s not that of a problem, but the BIOS could be not recognizing other CPUs than programmed into it.