This original files were found at http://code.google.com/p/matlab-gpib/
and cloned with the following command
hg clone https://code.google.com/p/matlab-gpib/
This code is distributed under GNU GPL v2 license
In Matlab switch to this directory and run
mex gpib_function.c dispatch.c -lgpib
Above will compile the proper Matlab interface, which apparently should happen by itself at the first execution of 'lgpib' within Matlab.
If you want to run it from network drive move resulting 'gpib_function.mexglx' to a computer dependent location.
See 'gpib_test.m' and 'HP8596E_take_data.m' for usage examples.