migration to new version of tomcat

Hi All 

I am using Tomcat 4.0.3 for my servlet application. Using this version of tomcat i just have to copy a folder with name " work" sub-folders WEB-INF/classes contain all my code; i think its clear to every one; 
Now i have install tomcat 4.1.18 and the above method not work;
can any body guide me where i have to make changes in configuration files of tomcat to make my application in working condition;

Thanx in advance.....

Mazhar Saeed