Helo Harshita,
There is no specific difference between 3.x and 7.x based on windows 7 and windows 8.
only difference is windows 8 doesnot support BEx 3.x because BEx 3.5 was not tested with windows 8 so we donot recommend and support BEx 3.5 on Windows 8.
this is already documented in my below KBa.
1846536 - BEx Analyzer 3.x & 7.x : Support for MS Excel 2013 and Microsoft Windows 8
Regards,
Arvind