Put this code inside "shoutlog.aspx" inside "/desktopmodules/ddnforge - shoutbox" folder
If you use the Smart-Thinker modules (thinking about the UserProfile module), you might want to link to a user profile, directly from the shout-box (ex here)
Edit ShoutLog.aspx and find the databinder with username, insert this instead.
<%# DataBinder.Eval(Container.DataItem, "username") %>