Ok Guys,I have fixed the problem.
Everything is up and running fine.
Let me say what I did.
Here are the steps:-
Open Control Panel > Folder Options > View > Enable Show hidden files and folders. > OK/Apply.
Go to My Computer > Open C:\ProgramData\Microsoft
Now double Click on eHome.There you will find Packages.If everything is fine(i.e.in normal condition) in a system then there should be four sub-folders under the Package folder-these are:-
1]ClientUpdate-includes ClientUpdate cab and DefaultGeoSettings file.
2]MCESpotlight-it contains a SpotlightResources.dll and MCESpotlight cab file.
3]SportsSchedule-it contains SportsSchedule.mxf and SportsSchedule.enc files.
4]SportsTemplate-it has three cab files namely-ScheduleSupplement,SportsTemplate and SportsTemplateCore.There are also ScheduleSupplement.mxf,FoxSports.sdp and Microsoft.MediaCenter.Sports.UI.dll files.
Now all these above are created flawlessly if the EPG downloading is excellent and during the initial MCE set up.
So another suspected item remains apart from Package folder.It's the EPG.You can locate it under:-C:\ProgramData\Microsoft\eHome\EPG
Next I deleted both these folders;(You can delete Package folder only also-as a trial error method)i.e. Package and EPG.Reboot the System.Open Vista MCE >Settings>General>Windows Media Center Setup>Run Set up again
Waw! under the Online Media I am now finding explore and Program Library.So long the explore was missing.Program Library icludes Games.
Now clicking the explore you will find <Showcase>,<tv+movies>,<music+radio>,<news+sports> etc all are functioning.
You can do the same in case of 32 bit version also,if you face the similar situation.
Otherthings you can do apart from the above solution:-
a simple reinstallation,or copy the Package folder contents from any 32/64 bit machine where all the above components are funtional and simply replace the damaged Package folder.
And finally you need a small thing-Adobe flash player.Just visit to the concerned site and download and install the latest flash player.
Remember 64Bit Vista Ultimate has less contents under the Online Media than the 32 Bit version.It's normal.Don't worry.I am now enjoying cool new experience-hope you will too.