With the Web thin client, your program executes on the server, and only the user interface displays on the client.
The recommended method of executing the ACUCOBOL-GT Web Thin Client is with the <OBJECT> tag. See Using the OBJECT Tag.
The browser loads the Web thin client (which you recall is an ActiveX control) and feeds it the data coming from the Web server. In this context there is no concept of a command line.
To pass "command line" style parameters to the ACUCOBOL-GT Web Thin Client, you use the AcuCommandLine property of the <OBJECT> tag when you invoke the application in your Web page.
The Web think client only supports a single instance. Internet Explorer 6 introduced tabs that allow more than on web page to e displayed in a single browser. IE 6 and 7 load all tabs into the same process. IE 8 loads the first couple of tabs in separate processes but eventually (depending on the client computer's resources) will start loading subsequent tabs in a previous tab's process. So it may be possible to run more than one Think Client application in a single Internet Explorer window using version 8.
Whenever a user attempts to run a second instance of the Web Thin Client in a process, the second instance of the control will detect this condition and enter a blocked state. This means the acuthin DLLs haven't been loaded and the Think Client application is not executing on this page/tab. The Web Thin Client control has properties to detect this state and give the developer choices in how to handle it. See Object interface for the Web thin client.