To view WAP pages from your desktop, you need a program like WinWAP. Usually when you hit a website saying that you're denied accesss, it's usually because you've accessed the website from a desktop browser so you get re-directed to the error page.
Never seen one which states BlackBerry only but I imagine it's not that hard to do. The simplest and crudest way would be to check the browser and see if it's the BB Browser accessing the server.
There's some PHP code here to detect between HTML and WML browsers: http://www.thewirelessfaq.com/4.6.asp
That should give you the idea on how to get started.