Items.h (and any file with a .h or .cpp) extension are C++ source files, not SQL commands.
To have the change to Items.h take effect, you need to re-compile the server using a compiler such as Visual C++ 2008, if you are using Windows.
There is a guide on how to compile the source code:
http://www.eqemulator.net/wiki/wikka.php?wakka=VS2008
But it would be easier for you to keep all your Item IDs below 120,000, then you won't have to recompile.