Thanks ServerStorm for being helpful. I went through some tutorials and played with joomla code aswell which made something possible for me.
Different homepage as compared to other pages
M still playing on it to show new, events and spotlight widgets on homepage. Seems like i will surely achieve this.
Needs to have different banner on header according to the category of article.
Handled this with a bit joomla programming and was able to do that successfully.
Regarding rest of the thing, I have been through extensions and plugins available on internet with no luck. As am using joomla 2.5 and most of the plugins are old or either paid. Have been playing on its default theme (beez20) which do not have such functionality that i require, so I m searching on it. I was expecting some code snippets or extension/plugins to do these things. Things you have mentioned against my points are :
Admin have ability to post articles having jquery image galleries.
There are plugins already that have similar functionaility to jQuery’s image galleries. If you must use jQuery’s then you could write a plugin that does what you need.
I have installed JCEDITOR as default editor do not have any attractive thing. JCEDITOR has jquery accordion kind of functionality that makes it a bit interesting but still I am looking for gallery stuff.
Content approval by admin before article appears on frontend.
Yes you can do this.
I tried out some plugins, but most of them doesnt work for version I am using , and other seemed worthless when they have same functionality that joomla is providing by default. Let me explain a bit about this :
I will give publisher right to some users so they can post articles in joomla (that i know joomla already does). But I dont want them to appear on front end untill Super Admin approves them. They must remain unpublished until that. I know wordpress has these by default for post-comments but m stuck with joomla because of client requirement. (he just wants joomla)
Have to show login form where user is accessing member’s content (articles thats it)
This is possible to do directly from the Joomla permissions.
Yes, but that shows an error when user tries to access restricted content. I want a login form alongwith it. (I guess I will be able to do that with few research on joomla programming)
I need users to be able to login via gmail account and LDAP
Even I wonder why joomla has given these plugins by default (LDAP and gmail) though I dont find gmail working (It says we need to make user register with their gmail email and password - then whats the difference between joomla authentication and gmail authentication when user still needs to register?). 
Content versioning (about the changes made in arcles).
Even I doubt if joomla or other CMS has such stuff (version history means it should highlight changes that are made in content)
Last and very important thing is that I need TWO portals being managed with ONE joomla administration like if i want http://aud.edu/ and http://engr.aud.edu/ shall be managed via one joomla administration.
Have you done these stuff with joomla before? May be if you provide me some extensions references so I can try them also.
Thank you once again.