Based on this article
, you should be able to get to it as long as you're using BES and the BlackBerry Browser, since that apparently funnels traffic from the Blackberry to your BES then to its destination (intranet or internet).
The question is going to be whether you can get name resolution and the like; I suspect you'll be able to do so. If not, you might try going to the IP of the intranet server - depending on how the web server is configured, that may or may not work. I'm not going to get into the intricacies of how that's configured unless you can at least get an error message back from it.
You'll probably need to add a bookmark in the Blackberry browser for it and specify which browser mode to use as part of the bookmark (assuming that yours are similar to the Curve's behavior)