Make sure you have no missing libraries by running:

LD_LIBRARY_PATH=bin ldd bin/vguimatsurface.so 2>&1 | grep 'not found'

while in the game's directory. Keep in mind, that although fun^H^H^H^H^H^H that the game is 32-bit and you need to install the correct architecture version in case of 64-bit systems. Then, you can run ./portal.sh