UPDATE: As I suspected ... having more than one site in IIS was root cause of trouble, Once I uninstalled Sharepoint Server 2010 and its web sites from IIS, my Visual Studio 2010 debugger was able to "Auto-Attach" w3wp.exe process while debugging any application ... ( I really don't see any reason that even after disabling all other websites why still it was giving me error at first place ?? )
I know its not a solution, because I have to remove Sharepoint Server ... but at present its more important for me to work on that application then Sharepoint Server.
But I am still open for any suggestions which might help me to run both together ....
Thanks,
Jack