select ur radio button and click property window:
property --> Accessibility--> tabindex
Set ur tabindex number...for example u set 1 means wen u enter tab button..tab button goes to radio button...
For ur code:
<div class="table_column_85R">
<asp:RadioButtonList ID="rblStatus" runat="server" RepeatColumns="3" RepeatDirection="Horizontal"TabIndex="1" OnSelectedIndexChanged="rblStatus_SelectedIndexChanged" AutoPostBack="true">
<asp:ListItem Text="Inprogress" Value="5" />
<asp:ListItem Text="Extension" Value="3" />
<asp:ListItem Text="Completion" Value="2" />
</asp:RadioButtonList>
</div>
u change tab index no is 1...tat's all..
if it works correctly mark this as a solution....
Happy coding...