Alternating Item Style

<div class="MyImage"><img src="" /></div>
<div class="MyDescription">Blah...Blah...</div>

.MyItemStyle .MyImage {width:49%; float:left;}
.MyItemStyle .MyDescription {width:49%; float:right;}

.MyAltItemStyle .MyImage {width:49%; float:right;}
.MyAltItemStyle .MyDescription {width:49%; float:left;}

ItemStyle = "MyItemStyle"
AlternatingItemStyle = "MyAltItemStyle"

<asp:Repeater runat="server" ID="Repeater1" OnItemDataBound="Repeater1_ItemDataBound" />

public void Repeater1_ItemDataBound(Object sender, RepeaterItemEventArgs e)
{
    if (e.Item.ItemType == ListItemType.AlternatingItem)
    {
        // e.Item is an alternating item
    }
    else
    {
    }
}

<asp:GridView>
    <Columns>
        <asp:TemplateColumn>
            <%# Container.DataItemIndex % 2 == 0 ? Eval("Image") : Eval("Desc") %>
        </asp:TemplateColumn>
        <asp:TemplateColumn>
            <%# Container.DataItemIndex % 2 == 0 ? Eval("Desc") : Eval("Image") %>
        </asp:TemplateColumn>
    </Columns>
 </asp:GridView>

<asp:GridView>
    <Columns>
        <asp:TemplateColumn>
            <uc:Image Data='<%# Eval("Image") %>'
              Visible='<%# Container.DataItemIndex % 2 == 0 %>' />
            <uc:Description Data='<%# Eval("Description") %>'
              Visible='<%# Container.DataItemIndex % 2 != 0 %>' />
        </asp:TemplateColumn>
        <asp:TemplateColumn>
            <uc:Image Data='<%# Eval("Image") %>'
              Visible='<%# Container.DataItemIndex % 2 != 0 %>' />
            <uc:Description Data='<%# Eval("Description") %>'
              Visible='<%# Container.DataItemIndex % 2 == 0 %>' />
        </asp:TemplateColumn>
    </Columns>
 </asp:GridView>