Richard,

"Do you think that this instruction is valid without the development board, i.e. stand-alone 8051 with lcd ?"

Absolutley valid. Your development board must be having a memory mapped I/O scheme. And what you are trying is direct I/O. Both are possible to use with LCD - but in the memory mapped I/O scheme, P0 is the data In/Out port and the peripheral at whom this transaction is directed is based on the address decoding that is carried out. If you can give more details on the hardware setup then we can do a "combined" debugging.

Incidentally did you sleep well last week ;-)

Raghu