I use an ASUS P5LD2 SE. But I can't get a dual core until I download some driver or something.

Is it worth getting a new motherboard or should I try and find the correct driver ?.

If all you have to do is a BIOS update to run a Core 2, why buy a new board? Check here, http://support.asus.com/cpusupport/cpusupport.aspx?SLanguage=en-us&model=P5LD2 , and make sure you have the correct PCB version; the earlier ones apparently do not support Core 2 CPUs. If you have an early one, then you will have to buy a new board.