You cannot use any of the new Sandy Bridge CPUs - the socket is different and the chipset requirements differ.

You can downgrade to an i5  CPU if you must have Optimus support.

 Thanks for the information. for downgrading, which i5 model(hightest spec with lower heat generate) support by this chipset ? Is it possible to load mac osx 10.6(original) on L501x ? and lastly, I encounter a lot of problem with my copy of windows 7 (64bit), when installing software which not 64bit base, do you think it is possible to get dell to convert license of my copy of windows 7(64bit) to 32bit windows ?

 Thanks for the information. for downgrading, which i5 model(hightest spec with lower heat generate) support by this chipset ?

Any non-Sandy Bridge (first generation) i5 will work.

Is it possible to load mac osx 10.6(original) on L501x ?

Legally, no.

and lastly, I encounter a lot of problem with my copy of windows 7 (64bit), when installing software which not 64bit base, do you think it is possible to get dell to convert license of my copy of windows 7(64bit) to 32bit windows ?

No.  If you want to do this you'll need to buy the 32-bit version - before you do, realize Dell doesn't support it, so you'll need to find drivers on your own.