Modifying programs to use more than one copy at a time.

[TQN]

As I see in the ASM code, I think we only need to patch at 005580F1, from JNZ MSN.005582AC to JMP MSN.005582AC.
The C pesudo-code can be:

HANDLE hEvent = CreateEvent(NULL, TRUE, FALSE, "MSNMSGR");
if (NULL == hEvent)
    goto Error; // At addr 005582B3
else
{ 
    if (ERROR_ALREADY_EXISTS /* = 0xB7 */ != GetLastError())
        goto StartNewInstance; // At addr 005582AC
    else
    {
        // Wait until the first instance of MSN exited
        if (WAIT_FAILED /* = -1 */ == WaitForSingleObject(hEvent, INFINITE /* = -1 */))
            goto Error; // addr 005582B3
        FindWindow("MSNMSGRBlObj", NULL);
        // ..............
        // ..............
    }
}

Regards,