How to simulate the sample of RAMTester under ModelSim 6.1a?

I want to simulate the sample of RAMTester under ModelSim SE 6.1a.
I added the sdramctrl.v, ramtest.v, dcm_sys.v into the project and compiled them. In compiling module fifo16w16r_2048 there is a set of errors showing that “Error: …RAMTester/modelsim/ramtest.v(38): Net type of ‘din’ must be explicitly declared (default_nettype is "none")." After I commented the sentence of "default_nettype none”, there is no error. However, errors appear when “loading design”:
** Error: (vsim-3033) F:/test board/Samples/RAMTester/modelsim/ramtester/dcm_sys.v(44): Instantiation of ‘IBUFG’ failed. The design unit was not found.

There is a “Simulation” folder under the installation directory of opal kelly, which implies involving the, des_tf.v and okHostCalls_v2.v into the project.
However, with “okHostCalls_v2.v”, even the compilation can not be completed.
Please let me know what files should be added to set up the simulation for this example. Thanks!