iReports 4.0 Test Connection Failed

[Nagarajan Thangapandi]

Hi
I am using iReport4.0, I tried to connect the jtds driver for Ms Sql Server 2005 in iReports.
I am getting this error message:
ClassNotFoundError!
Msg: net.sourceforge.jtds.jdbc.Driver
Possible not found class: net.sourceforge.jtds.jdbc.Driver

Thanks
Nagarajan T.