Fixed header in GridViews

Firstly wrap your gridview in a div

<DIV style="OVERFLOW: auto; HEIGHT: 120px"><asp:GridView ... /></DIV>

Then in the GridView add a HeaderStyle:

<asp:GridView ID="MyGridView" runat="server">
<HeaderStyle CssClass="gridheader" />
</asp:GridView>

Then add the css class

.gridheader
{
background-color: white;
position:relative;
top:expression(this.offsetParent.scrollTop);
}

All done!