why dont you have both?
Radion button (without any text) and and image on it's side?
on the radiobutton property set the GroupName equal to everyone
<asp:RadioButton ID="RadioButton1" runat="server" GroupName="A1"
/><asp:image runat="server" id="Image1" /><br />
<asp:RadioButton ID="RadioButton2" runat="server" GroupName="A1"
/><asp:image runat="server" id="Image2" /><br />
<asp:RadioButton ID="RadioButton3" runat="server" GroupName="A1"
/><asp:image runat="server" id="Image3" /><br />
<asp:RadioButton ID="RadioButton4" runat="server" GroupName="A1"
/><asp:image runat="server" id="Image4" /><br />
<asp:RadioButton ID="RadioButton5" runat="server" GroupName="A1"
/><asp:image runat="server" id="Image5" />