populate dropdown list

I need to populate a dropdown list on the basis of other dropdown list. Both dropdwon list are datasourced with SQL datasource. I tried the SQL datasource where query . but it will need a post back. I dont want my form to be postback. I guess this is what AJAX is for but i really dont know how to get this with AJAX in a simple and quick way..... or it is not simple and quick ????

WebParts and ASP.NET AJAX 1.0

Here's a summary of WebParts support in ASP.NET AJAX 1.0. There are three different WebParts features:

1. Cross-browser drag and drop.
2. Modify WebParts page (drag and drop, minimize, restore, close, add, delete) without postback.
3. Update contents of WebPart without postback.

Cross-browser drag and drop is enabled by using the WebParts controls in the AJAX Futures CTP.
Modifying a WebParts page without postback is implemented by wrapping the WebPartManager and WebPartZones in an UpdatePanel. This was partially working in the July CTP, but it does not work and is not supported in ASP.NET AJAX 1.0. It may be supported in Orcas.

Updating the contents of a WebPart without postback is implemented by placing an UpdatePanel inside a WebPart. This is supported in the core ASP.NET AJAX Extensions 1.0. It should work with either the ASP.NET 2.0 WebParts controls, or the AJAX Futures CTP versions of the WebParts controls.

Enum

i had used that name space then also i'm getting this errorError 1 The type or namespace name 'UI' does not exist in the namespace 'System.Web' (are you missing an assembly reference?)

SSRS

give me the websites for sql server 2005 integration services interview questions ?

Find Version

Hi,

Can any one help me, How to find the version of ASP.NET?

Java script Vs ASP

what is the difference between java script and asp ?