The BaseValidator class defines the basic implementation needed for all Validation controls. There are 6 Validation Controls included in the ASP.NET 2.0 and ASP.NET 3.5 framework which validate controls to prevent the users from entering wrong data One
Two
Three
Four  

Step 1 :
write a javascript function with all validation you want to perform:
< script language="javascript" type="text/javascript" >
function IsValidBetAmount(sender, args) {
// alert(args.Value);
var betValue = eval(args.Value);
if (betValue % 1000 == 0) {
args.IsValid = true;
return
}
else
args.IsValid = false;
}
< /script >

Step 2 :
Set a control and a custom validator to perform the test
< asp:TextBox runat="server" ID="txtBetAmount" CssClass="txtBox" ValidationGroup="vgBetAmount" >< /asp:TextBox >
< asp:CustomValidator runat="server" ID="cvBetAmount" ControlToValidate="txtBetAmount" ValidationGroup="vgBetAmount" ClientValidationFunction="IsValidBetAmount" ErrorMessage="Bet should be round of 1000." ValidateEmptyText="true" / >

Step 3 :
Set a action button where you need to perfom the validation
< asp:Button runat="server" ID="btnSubmitBet" Text="Bet" CssClass="button" ValidationGroup="vgBetAmount" OnClick="btnSubmitBet_Click" / >