Installing Web Access on a second machine would require a second license, but it sounds like that isn't necessary in your case.  What you want is a second instance of the Web Access web application on that same machine.  In order to do that, you would just create a new Application in IIS.  Since you want it to use different settings from the first, you would want to point it to a copy of the Web Files folder in Web Access (otherwise they will read from the same configuration files).  If you're not familiar with IIS it can be tricky to copy over all of the application settings from the first one.  Also, since the Web Access installation doesn't know about your copy of the files, it won't touch them when you apply any updates, so you'll have to handle that yourself.