New to install shield, please help

[malepativ]

I am new to install shield and trying to create a install shield package. Everything is good, copying files and creating registries etc. However I want to check the windows wether xP or vista and then install user profiles according to the OS customer have. I hope everybody is doing that. I donot find any information or documentation or tutorial how to do it. I just some script code like the following. How should I call this function?. Please enlighten me.
If I write the code install script "setup.rul" then when should I call this function and how. I think I need to read more, however I am not finding the enough documentation in the help files.
Please somebody reply
Malepati


/===========================================================================
//
// File Name: Setup.rul
//
// Description: Blank setup main script file
//
// Comments: Blank setup is an empty setup project. If you want to
// create a new project via. step-by step instructions use the
// Project Assistant.
//
//===========================================================================

// Included header files ----------------------------------------------------
#include "ifx.h"
// Include Isrt.h for built-in InstallScript function prototypes.
#include "isrt.h"

// Include Iswi.h for Windows Installer API function prototypes and constants.
#include "iswi.h"

// Note: In order to have your InstallScript function executed as a custom
// action by the Windows Installer, it must be prototyped as an
// entry-point function.

// The keyword export identifies MyFunction() as an entry-point function.
// The argument it accepts must be a handle to the Installer database.

/* export prototype MyFunction(HWND); */
// Create a log file on the C drive so that
// the install can log information to it. This is a convenient
// location for tech support to find it.
export prototype void LogSystemInfo();

//Send system information to log file
function void LogSystemInfo()
STRING svComputerName, svDate, svOS, svOSSP, svWinMajor, svWinMinor;
NUMBER nvDate, nvOS, nvOSSP, nWinMajor, nWinMinor;
begin

// Get the operating system.
nvOS = SYSINFO.nISOSL;
switch (nvOS)
case ISOSL_WIN2000:
svOS = "Windows 2000";
case ISOSL_WINXP:
svOS = "Windows XP";
MessageBox("Installing in windows xp",INFORMATION);
case ISOSL_WINSERVER2003:
svOS = "Windows 2003 Server";
case ISOSL_WINVISTA:
svOS = "Windows Vista";
default:
svOS = "Invalid OS";
endswitch;

end;

[chbiki]

if you have a msi basic project your project is composed of many features, each feature has the option "condition", try to set this option to "VersionNT<600" for not Win Vista system...

[malepativ]

I have Installscript MSI project and depending upon the Windows OS I need to set the path's for my program. Some of them are environmental variables and some of them are system variables. I don't know where to approach. Why does Install shiled is lacking good documentation?. Anybody please point me to the good document or tutorials. The tutorials that the documentation has for simple install projects and not for adavanced install projects, I guess.
Thanks for any help.
Malepati