Hello minh li,
To get that kind of URL, one possibility is to redefine your own portal container.
Read more here : http://community.jboss.org/wiki/Portalcontainers
You can also have a look at the example provided in the source code : http://anonsvn.jboss.org/repos/gatein/portal/trunk/examples/portal/
Firstly i think, if you want to use Gatein for a while, you may have to read the document.
Third, actually, no matter what means "steel" in your context, you can use administrator tools to set "steel" as index page of your portal. You may have try it by your self.
Fourth, people can tell you where to find the answer, but they can not teach you how to implement it step by step. You may find it by your self. So that means, you have to read english document, although it may be difficult for you.
Any way, i speak chinese, you have my email. If you really need help urgently, you can write me.