Hello,

The key here is using the client side ValueListSelChangeHandler client-side event - it gets fired whenever you are changing the selection from the dropdown for the respective column. Inside the client-side event handler you get three parametes - gridID, valueListID and cellID. You can get the dropdown instance from valueListID and get its selectedindex - and then use the client-side API of the grid to change cell values in other columns  based on the selection in the first one.

Example:

 <igtbl:UltraWebGrid ID="UltraWebGrid1" runat="server" DataSourceID="AccessDataSource1"
        Height="200px" OnInitializeLayout="UltraWebGrid1_InitializeLayout" Width="325px">
        <Bands>
            <igtbl:UltraGridBand>
                <HeaderStyle Height="50px" />
                <Columns>
                    <igtbl:UltraGridColumn BaseColumnName="ReorderLevel" DataType="System.Int16" IsBound="True"
                        Key="ReorderLevel" Type="DropDownList">
                        <Header Caption="ReorderLevel">
                            <RowLayoutColumnInfo OriginX="8" />
                        </Header>
                        <Footer>
                            <RowLayoutColumnInfo OriginX="8" />
                        </Footer>
                        <ValueList>
                            <ValueListItems>
                                <igtbl:ValueListItem DisplayText="Text1" DataValue="1" />
                                <igtbl:ValueListItem DisplayText="Text2" DataValue="1" />
                                <igtbl:ValueListItem DisplayText="Text3" DataValue="1" />
                            </ValueListItems>
                        </ValueList>
                    </igtbl:UltraGridColumn>
                    <igtbl:UltraGridColumn BaseColumnName="Discontinued" DataType="System.Boolean" IsBound="True"
                        Key="Discontinued" Type="CheckBox">
                        <Header Caption="Discontinued">
                            <RowLayoutColumnInfo OriginX="9" />
                        </Header>
                        <Footer>
                            <RowLayoutColumnInfo OriginX="9" />
                        </Footer>
                    </igtbl:UltraGridColumn>
                </Columns>
                <AddNewRow View="NotSet" Visible="NotSet">
                </AddNewRow>
            </igtbl:UltraGridBand>
        </Bands>
        <DisplayLayout BorderCollapseDefault="Separate" Name="UltraWebGrid1" RowHeightDefault="20px" AllowUpdateDefault="Yes"
            Version="4.00">
            <ClientSideEvents ValueListSelChangeHandler="cellUpdate" />
            <FrameStyle BorderStyle="Solid" BorderWidth="1px" Font-Names="Verdana" Font-Size="8pt"
                Height="200px" Width="325px">
            </FrameStyle>
            <Pager>
                <PagerStyle BackColor="LightGray" BorderStyle="Solid" BorderWidth="1px">
                    <BorderDetails ColorLeft="White" ColorTop="White" />
                </PagerStyle>
            </Pager>
            <EditCellStyleDefault BorderStyle="None" BorderWidth="0px">
            </EditCellStyleDefault>
            <HeaderStyleDefault BackColor="LightGray" BorderStyle="Solid">
                <BorderDetails ColorLeft="White" ColorTop="White" />
            </HeaderStyleDefault>
            <RowStyleDefault BackColor="White" BorderColor="Gray" BorderStyle="Solid" BorderWidth="1px"
                Font-Names="Verdana" Font-Size="8pt">
                <Padding Left="3px" />
                <BorderDetails ColorLeft="White" ColorTop="White" />
            </RowStyleDefault>
            <AddNewBox>
                <BoxStyle BackColor="LightGray" BorderStyle="Solid" BorderWidth="1px">
                    <BorderDetails ColorLeft="White" ColorTop="White" />
                </BoxStyle>
            </AddNewBox>
            <ActivationObject BorderColor="" BorderWidth="">
            </ActivationObject>
        </DisplayLayout>
    </igtbl:UltraWebGrid>
    <asp:AccessDataSource ID="AccessDataSource1" runat="server" DataFile="~/App_Data/Nwind.mdb"
        SelectCommand="SELECT * FROM [Products]"></asp:AccessDataSource>
       
     <script type="text/javascript">

         function cellUpdate(gridID, valueListID, cellID)
         {
             var valueList = document.getElementById(valueListID);
             if (valueList.selectedIndex == 0) {
                 // do something.. like check checkbox
             }
             else {
                // uncheck checkbox
             }
         }
    
     </script>   

A very good thread that can help you with CSOM and how to change values is this one:

http://forums.infragistics.com/forums/p/1156/11700.aspx#11700

HTH,