Tomcat5.5 do not enable admin or manager access by default. We have to manully edit tomcat-users.xml to allow admin access. VI your tomcat-users.xml in tomcat conf folder, content is something like following

<?xml version='1.0' encoding='utf-8'?>
<tomcat-users>
  <role rolename="tomcat"/>
  <role rolename="role1"/>
  <user username="tomcat" password="tomcat" roles="tomcat"/>
  <user username="both" password="tomcat" roles="tomcat,role1"/>
  <user username="role1" password="tomcat" roles="role1"/>
</tomcat-users>

Tomcat only create a tomcat user for normal access, we have to modify a bit like following

<?xml version='1.0' encoding='utf-8'?>
<tomcat-users>
  <role rolename="manager"/>
  <role rolename="tomcat"/>
  <role rolename="admin"/>
  <role rolename="role1"/>
  <user username="both" password="tomcat" roles="tomcat,role1"/>
  <user username="tomcat" password="tomcat" roles="tomcat"/>
  <user username="admin" password="admin" roles="admin,manager"/>
  <user username="role1" password="tomcat" roles="role1"/>
</tomcat-users>

Saved it and restart tomcat, now we can access tomcat admin or maneger page with user:admin password:admin.