For some reason none of these DIVs render disabled. Oddly enough, when I set Enabled="False" on the .NET Panel, then it renders the Panel as a DIV with disabled="disabled", which works great.
Here's my doctype:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<div id="Div1" disabled="disabled">
<input type="text" value="blah" />
</div>
<div id="disableMe" disabled="disabled">
<input type="text" value="blah" />
<asp:Panel runat="server">
<asp:RadioButtonList runat="server">
<asp:ListItem Text="Item1" Selected="True" />
<asp:ListItem Text="Item2" />
</asp:RadioButtonList>
<asp:TextBox runat="server" Text="Hello World" />
</asp:Panel>
</div>