1) Why didn't you just post the URL http://www.eduardlid.net/nicolas/hospedaje/hospedaje.html to make it easy for people to go right to the page in question. Any minute you save us will be use to try to solve the issue at hand.
2) Your CSS ex4.css cannot be found. So you need to solve the path.
3) Create a container div(<div id="imgecontainer">....your images go here</div>) then:
- solution a: set its let and right margins to the specific pixels value you desire.
margin:0 40px; / 0 for top and bottom, 40px fro left and right margins. Change to whatever values /
- solution b: set the width of #imagecontainer to a certain percentage of the page width then set its margins to auto
width:90%; / change to whatever percentage can accommodate your images /