There's also a "manual" way to make a link in a post here on WoWI.
It would look like this (in the "Reply to Thread" text box):
[ url="http://www.wowinterface.com/downloads/info13001-CurrencyTracker.html" ]CurrencyTracker[ /url ]
I had to add spaces so it would show correctly, and the spaces are after each leading bracket and before each trailing bracket. The URL is a direct copy / paste from your browser address bar. Don't forget the quote marks. It doesn't work without them.
If done correctly, this is what you'll see in your post:
CurrencyTracker
I think it's straight BBCode, and that's why it works on WoWI's forums.