Put the DLL in the root directory of mIRC and then add the following code to aliases.ini

Code:
ie {
  window -aek0p @Browser 0 0 800 600
  var %ws.1 $dll(nHTMLn.dll,attach,$window(@Browser).hwnd) 
  var %ws.2 $dll(nHTMLn.dll,navigate,http://iserv.com.au/)
  editbox @Browser http://iserv.com.au/
}
That allows the page to open (in this example, my website) when you type /ie on a channel or status or whereever.

I then added this in a remotes file as an optional extra:

Code:
ON *:INPUT:@Browser: {
  var %ws.1 $dll(nHTMLn.dll,attach,$window(@Browser).hwnd) 
  var %ws.2 $dll(nHTMLn.dll,navigate,$1)
  if (http:// isin $1) {
    editbox @Browser $1
  }
  if (http !isin $1 && .htm !isin $1 && .asp !isin $1 && .cfm !isin $1 && .pl !isin $1 &&.php !isin $1) {
    editbox @Browser http:// $+ $1 $+ /
  }
  if (http isin $1 && .htm !isin $1 && .asp !isin $1 && .cfm !isin $1 && .pl !isin $1 &&.php !isin $1) {
    editbox @Browser $1
  }
  if (http !isin $1 && .htm isin $1 || .asp isin $1 || .cfm isin $1 || .pl isin $1 || .php isin $1) {
    editbox @Browser http:// $+ $1 $+ /
  }
  if (http isin $1 && .htm isin $1 || .asp isin $1 || .cfm isin $1 || .pl isin $1 || .php isin $1) {
    editbox @Browser $1
  }
}
This lets you navigate to new URLs using the editbox in the browser window. The code could be more efficient but it does work, with the addition that URLs get "completed" similar to the way a web browser does it.

The downside seems to be that the mIRC editbox cuts off the bottom 11 pixels of the page, including the 'down' arrow in the scrollbar but that's life.