Have a look at the IIS URL Rewrite module. It will do exactly what you are looking for without having to write any code. This article explains it pretty clear:
http://learn.iis.net/page.aspx/461/creating-rewrite-rules-for-the-url-rewrite-module/
You can download IIS URL Rewrite here: http://www.iis.net/download/urlrewrite
Please do your question in Portuguese.
Não esqueça de usar o componente </> na barra para posta seu código. Microsoft MCPD,MCTS,MCC