If you're trying to post a link on AB, the important thing to remember is that you need to quote the full URL, including the 'http' bit.
A slight variation on Spudqueen's technique is this. (It's easiest if you've got two separate tabs, or windows, open. One for the page you want to link to and one for your AB post):
In the tab displaying the page you want to link to, right-click in the address bar at the top of the page. (This will highlight the URL). Select 'copy'. In the tab for your AB post, click to place the cursor where you want the link to appear. Right-click and select 'paste'.
Chris