You can run external programs using one of several commands:- Exec, ExecShell, ExecWait, nsExec::Exec, nsExec::ExecToLog, nsExec::ExecToStack. The first three Exec commands may produce a dos command prompt window, the latter three will not. In fact the very last two can capture text output from the program u launch and show it in the detail window or add it to the stack for you to retrieve.
You may want to find out how to run your other setup programs silently so it looks like you just have your nsis installer running. This page might help