Anand:
But my question is what about the emulator which supports only 256K and my code is 480K. How to emulate my code?

Dennis:
There are 8051 derivatives that support large code spaces without banking (Dallas parts, I'm sure there are others).
Noteably Philips Mx and 669

When you have to rethink your tools because of the size of the project, this is a good time to rethink the processor you're using: is it the best choice for the task at hand?
"my code is 480K " sounds as if the '51 is the wrong choice.

Erik