Aha, I see the problem. The sapinstgui is not related to installing SAPGUI. I know, the names are confusing. That is a tool that is used for installing an SAP server, not the client. Furthermore, it's a tool not intended to be executed directly, but rather called from another tool.
Can you clarify, are you talking about installing the SAP NetWeaver server, or are you trying to install the SAPGUI client? Either way, you are not using the correct tool, but it looks to me like you are trying to install the server.
Do you have access to the installation guides? They will walk you through the correct process.
--Matt