This depends on how you access the different machines. If you just want to run a web test on different web server machines you can use one client that runs the same test on different server machines.
' run test
' run same test
If you actually want to run the test on machine1, machine2, etc. I mean such as start browser (or any other application) on machine1, do some tests, start browser on machine2, do some tests then you will have to install QTP on machine1 and 2 and start the test there either "by hand", by AOM or via Quality Center.
Furthermore if you have many tests you can reduce testing time running the tests on multiple machines at the same time.