If this is an older application it might be more work. I.e. EJB2 need a lot of XML and often vendor specific descriptors which need to be migrated.
So it depends extremly on your application and there is no general way to do it.
If you use XDocelet for and old application and you don't have a lot of vendor specific optimizations it might be easier.
As long as you have such general questions I think you will not get any better answers.
Thanks fink for your response. This time, while migrating my application, I have come across JAAS authentication failure issue in my application. I have checked "custom login module creation" process in JBOSS AS 7.1. My application will be run on other web servers like weblogic too. What changes will I need to do to keep authentication process same across application servers??? I see that security documentation section under "Migrating applications from weblogic to JBOSS" in JBOSS guide is incomplete. Any help??
We have done a similar thing about 1 and a half year ago. We migrated our app from JBoss 4 to JBoss 7. It was quire a lot of work but mostly on the web side due to RichFaces 3.x --> 4.x migration. Except from the web it wasn't that much but it required a lot of knowledge. If you say you are totally new to this thing I suggest start studying first, if you wanna do a good job. This I can say from my experience.
Login modules are configures in standalone.xml in jboss as 7. There ara standard login modules (http://docs.jboss.org/teiid/7.3.0.Final/developer-guide/en-US/html/custom_login_modules.html). If your app requires custom login modules you should find here something: https://developer.jboss.org/wiki/JBossAS7SecurityCustomLoginModules
I don't have experience with other as, but I suppose if you keep your authentication standard through JAAS you won't have problems, you will just have to specify authentication and authorization parameters.
Like Wolf-Dieter Fink said, try with more specific questions.