I have installed and tested on WindowsXP. For rest of the operating systems i am not sure it will work or not. Step1: First of all install Visual Studio 6.0. Otherwise during OPNET installati on you will get an Error: no c++ compiler found! a) Goto the path \OPNET Installation\Visual Studio 6.0\CD1 and Run the "sET UP" file. b) Press next/ok on each popup window with default settings unless otherwis e stated. c) Enter Key: 352-0200363 d) If may see a window reboot option then restart the WindowXP and continue to next steps. e) At one stage "setup environment variable" popup window will appear, sele ct the checkbox of Registering Environment Variables and press OK. f) During installation at 2-3 places you will see a message "Setup could no t open the file", igrone that message and continue. g) After complete installation restart the system. h) On command prompt type cl and press enter. If you see the following mess age "Microsoft 32 bit c/c++ optimizing compiler", it mean Visual Studio is c orrectly installed and working fine. Step2: OPNET Simulator has three files which need to be installed in a proper se quence. a) Goto the path \OPNET Installation\OPNET.Modeler.14.0.A.PL3 and Run the " modeler_140A_PL3_6313_win" file. b) Press next/ok on each popup window with default settings unless otherwis e stated. c) After successful installation Goto the path \OPNET Installation\OPNET.Mo deler.14.0.A.PL3\Crack and Run the "OPNET.Modeler.License.Maker.Univarsal-FFS" f ile. d) You will see a popup window of License Maker, press ok to continue. e) You will see another window having message License is created, press ok and restart the system. f) Then for second file, Goto the path \OPNET Installation\OPNET.Modeler.14 .0.A.PL3 and Run the "models_140A_PL3_17Oct07_win" file. g) Click next on all popup windows with default settings. h) Then for third file, Goto the path \OPNET Installation\OPNET.Modeler.14. 0.A.PL3 and Run the "modeler_docs_140A_PL2_24-Sep-2007_win" file. Restart the system and Enjoy the OPNET Simulator. To run the OPNET click start>programs>OPNET Modelor 14.0>OPNET Modelor 14.0. Go through some basic tutorials to learn the simulator. By default all the project files which you will prepare, store at C:\Documents a nd Settings\working user\op_models Note: If you see a message related to license just ignore and run the Step2c aga in, it will work fine again.