Hi Ranga,
I could be wrong, but I don't believe Excel actually rounds past the 15th digit, but truncates. I'm pretty sure you're not getting past the 15 digit limitation. You might find these interesting:
http://support.microsoft.com/kb/78113
http://support.microsoft.com/kb/158071
http://blogs.msdn.com/excel/archive/...g-answers.aspx
Mark