Landing pages…

Hi, I want to create a landing page for my site where by if anyone goes to mysite.com or mysite.com/random-page they get redirected to a custom landing page with a small welcome message, a login form and a picture/logo.

In effect, like facebook, where as you cant actually access anything (except T&C’s etc.) without first being a member of the site.

I have looked at and downloaded loads of “landing page” plugins but I cant seem to get what I need from them.. (probably me totally overlooking something as usual)

I create a page, save it and well.. that’s it..
So as you can probably tell, I am a bit of a noob on this so all help and idiot guides would be appreciated. =D

Thanks.