Create alert dialog window once particular user login-in.

Hi,

I'm trying to create a alert dialog window which has particular data in tabular format and shows for particular user group login's ARAS.

I'm checking the default.aspx,setup.aspx but don't know exactly where to embed so that it checks the login crendentials and leads to alert dialog window .

How to do and Where to embed the code to achieve this particular task.

Thanks,

Shantha.