Andrea, thank you very much for your answer,
I modify in my web site a file to include the request that you mentioned in your post, it work properly, you can see it at http://sintegralesa.org , please select the "Solicite Información" arrow at the left menu, you will see it at the end of the rigth section. (this site is designed in Spanish languaje).
The code is the same that I used in moodle:
<iframe src="http://sintegralesa.org/Guia Participante/guia.htm" frameborder="1" width="550" height="450" />
Thank you for your help,