It could be done but you would be better off looking at url rewriting.
take for example this link on my site :
http://www.dbnetsolutions.co.uk/Solu...iteDesign.aspx
What actually happens is that the server script gets the page request looks up the url in a database then returns the content which is based on another page.
http://www.dbnetsolutions.co.uk/contentitem.aspx?id=6
If you have more complex architecture in the case of a forum you would have to come up with another way to write your url's but the process is the same.