Exemplo do colega Fernando Boeno,achei bem legal.
https://dl.dropboxusercontent.com/u/90217826/Porcentagem%20em%20Form.rar
Outro modelinho
https://dl.dropboxusercontent.com/u/90217826/Porcentagem.rar
https://dl.dropboxusercontent.com/u/90217826/Porcentagem%20em%20Form.rar
Outro modelinho
https://dl.dropboxusercontent.com/u/90217826/Porcentagem.rar