Visual Studio 2010 - Web Deploy - Customise

I've got an ASP.Net application that I'm trying to deploy using Web Deploy to IIS 7.5.

I'm using 7.5 Express as the Development environment.

I'm having trouble deploying an Application Pool or at a minimum setting an Application Pool that's already on the IIS 7.5 Server.

Everything I've read has just confused me.

I believe best practice is to have the App Pool already setup on the Destination Server, setting the Published App to use this App Pool.

Is this correct?  How do I go about doing this I'd prefer to stay within the 2010 UI if possible.

Thanks