Hi Leena,
You can get the trial version of Websphere 4.0 from the IBms site.
The Websphere 4.0 comes with a Application Assembly Tool. AAT is a tool for assembling application from application components and modifying the J2EE discriptors for these components. We use AAT to create J2EE Application form J2EE Modules. The J2EE module consists of Web Module, EJB Module and Clinet Application Module. We create an .ear which comprises of these modules with the help of AAT.