I just want to share this with anyone having this problem.
Despite setting the server.xml netry for the context and, having the correct directory structure, the servlet login wouldn't load and kept giving a 404 error.
I managed to get it right by setting the web.xml file this way :
<?xml version="1.0" encoding="ISO-8859-1"?>
PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
I don't know if this makes any sense, but the node <url-pattern> did it and it works now.