This is kind of hacking eclipse and you can get into trouble doing this but this should work:
Open the navigator view and find that there is a .settings folder under your project expand it and then open the file: org.eclipse.wst.common.project.facet.core.xml you should see a line that says:
<installed facet="jst.web" version="2.5"/>
Change that to 2.4 and save.
Just make sure that your project isn’t using anything specific for 2.5 and you should be good.
Also check your web.xml has the correct configuration:
<web-app version="2.4"
xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">