As a former WebSphere Portal Developer at IBM, who has worked on projects using Rational Application Developer 6.0 with Portal 6.0, I can say with authority that there is no 'embedded' test environment for Portal 6.0 when I was working with RAD 6.0.
The "Portal 6.0" test environment you see in the Launchpad probably only installs a 'stand-alone' installation of Portal 6.0 on your computer, with the usual defaults.
In other words, unlike Portal 5.1, Portal 6.0 does not have test environment, and when I last checked, RAD 7.0 was not planning have an embedded test environment either. You basically have to install a 'stand-alone' Portal 6.0 stack on your laptop (which is pretty easy using all the defaults, installing on Windows), and just run RAD and Portal separately.
People in my group have mentioned the words "Remote Server Attach" when it came to 'hooking up' RAD to Portal 6.0. Maybe better tooling is there in RAD 7.0 to deal with this, I don't know. I do know that there are ways of remote-deploying a portlet from RAD to Portal; I've just never tried them.
Another resource to try is the IBM developerWorks forums for Portal. Sometimes the IBM Portal Software Group will be on there, and certainly, you'll get more WebSphere Portal-specific information. I don't remember the exact URL, but if you Google 'IBM' and 'developerWorks',
you should find it. Then do a search in both the Forum and in the Tech Articles.
The other alternative is to use Portal 5.1 as the previous poster suggested. If it's a JSR 168 portlet, and you're not using a lot of the IBM-specific extensions and functionality, a lot of the stuff will be the same.
[ August 01, 2007: Message edited by: Jimmy Ho ]