I want to modify the diffrent steps to create a new workflow, so I want to know the diffrent classes(.java) and files( .xml , .jsp , .css and .dtd ..) and the relation between them, that i should modify to realize this.
Depending on your timescales you may want to wait until 1.3 is released as this process is going to become much easier. Wizards will be configured so it's going to be much easier to swap in/out custom pages and implementations.
If you can wait until 1.3 (end of May timeframe) then you'll need to change projects/web-client/source/web/jsp/wizard/new-rule/action-simple-workflow.jsp. This page is loaded by the org.alfresco.web.bean.wizard.NewRuleWizard class, which you'll also need to customise.
You will also need to customize the server side action which can be found in org.alfresco.repo.action.executer.SimpleWorkflowActionExecuter.
