Execute program and capture output

you can redirect the output to a file.
Then read the file to get output.

exec("NET USER > out.txt");

read("out.txt");

Yeah, I know, but I was thinking more of redirecting the standard output (con) to my own stream or buffer. This way I don't have to go via another file.

http://www.codeguru.com/console/QuickWin.shtml

Check out the MSDN

This deals with consoles
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/fileio/hh/winbase/conchar_3vg3.asp

and

this deals with processes

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dllproc/hh/winbase/prothred_3mgj.asp

The most interesting function is CreateProcess()

If you "really" need help I'll give you a sample; currently I'm using QNX and is quite impossible to write a program for you on my machine

// Open the target file. Specify the ability to inherit the handle.
SECURITY_ATTRIBUTES sa = { sizeof(SECURITY_ATTRIBUTES), NULL, TRUE };
HANDLE hOutputFile = CreateFile("OutputFile", GENERIC_ALL, 0, &sa, CREATE_ALWAYS, 0, 0); // Tell the new process to use the file as the standard output.
STARTUPINFO si = {0};
si.dwFlags = STARTF_USESTDHANDLES;
si.hStdOutput = hOutputFile; // Start the process.
PROCESSINFORMATION pi = {0};
HANDLE hProcess = CreateProcess("file.exe", NULL, NULL, NULL, TRUE, 0, NULL, NULL, &si, &pi); // Don't forget.
CloseHandle(hOutputFile);
CloseHandle(hProcess);

oops, it got all messed up. You can read it here:
http://www.geocities.com/assaflavie/faqs/redirecting_std_output.txt

Thanks everybody.

The solution proposed by jkr provided exactly what I was trying to do, so I'm awarding the points to him.

Note: _popen( "net user" ) should read _popen( "net user", "r");