In the following code loadSummaryData() is quite a slow SQL query and
it prevents the page from displaying until the query has finished. I
want the user to be able to log on and see the page (i.e in this
example the "is logged on" message) before loadSummaryData() executes.
Is there a way to do this?

if (!IsPostBack)
{
    lblMessages.Text = loEmployee.employeeFName + " is logged on.";
    loadSummaryData();
}
else
{
}