You need to download the datasheet for your processor from Microchip. Then you need to read the section on EEPROM data memory.
This will explain how the 1K of memory is addressed.

The write command should work fine but probably can only access the first 256 bytes.

I use assembly subroutines to allow access to the full 1K memory. The datasheet shows exactly how to do this in assembly. I am using the PIC18F2525.

-Jim