I tried to integrate Atlas into WebPart a couple of days ago but failed. Atlas is a great AJAX framework from Microsoft, but it isn't compatible with SharePoint 2007 for now, what a pity.

But your customers always have this kind of complain, "The page will fully reload when I just click one button in the WebPart, I just wanna perform a very simple action but I have to wait until the page load complete." So, how can you handle this?

As you've known, there is a built-in feature called client callback in ASP.NET 2.0, which allows you call server method from client side without causing the page refresh, and SharePoint2007 is built upon ASP.NET 2.0 framework, so we can use this feature to support AJAX in WebPart.

In the following steps, I'm gonna show you how to get server date from client in a WebPart.
[If you are not familiar with Client Callback feature in ASP.NET 2.0 yet, I strongly recommend you read this article first]

1. Start up VS.NET 2005 and create a Class Library project.

2. Add System.Web.dll to the project reference.

3. Create a Class with a name you expect, which inherit from System.Web.UI.WebControls.WebParts.WebPart and implement System.Web.UI.ICallbackEventHandler interface.

4. Override CreateChildControls to create some controls.

5. Override OnLoad to regist related JavaScript to client.

6. Override RenderContents or Render to render WebPart to browser.

7. Implement ICallbackEventHandler members.

The source code is here:

using System;
using System.Text;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls.WebParts;

namespace SPS2007.Research.WebParts
{
    public class AjaxPart : WebPart, ICallbackEventHandler
    {
        private string strCallResult;
        private HtmlInputText tbResult;
        private HtmlButton btnCall;

        public AjaxPart()
        {
            
        }

        protected override void CreateChildControls()
        {
            base.CreateChildControls();

            tbResult = new HtmlInputText();
            tbResult.ID = "myTextBox";
            btnCall = new HtmlButton();
            btnCall.InnerText = "GetServerDate";
            btnCall.Attributes.Add("OnClick", "javascript:InvokeMethod();");
            this.Controls.Add(tbResult);
            this.Controls.Add(btnCall);
        }

        protected override void OnLoad(EventArgs e)
        {
            if ((this.Page != null) && !this.Page.IsCallback)
            {
                ClientScriptManager scriptManager = this.Page.ClientScript;

                string eventRef = scriptManager.GetCallbackEventReference(this, "argVal", "OnCallComplete", "ctxVal", "OnErrorOccurs", true);

                StringBuilder sb = new StringBuilder();

                sb.Append("function InvokeMethod(argVal,ctxVal)");
                sb.Append(Environment.NewLine);
                sb.Append("{");
                sb.Append(Environment.NewLine);
                sb.Append(eventRef);
                sb.Append(Environment.NewLine);
                sb.Append("}");
                sb.Append(Environment.NewLine);

                HtmlInputText textBox = this.FindControl("myTextBox") as HtmlInputText;

                sb.Append("function OnCallComplete(result,context)");
                sb.Append(Environment.NewLine);
                sb.Append("{");
                sb.Append(Environment.NewLine);
                sb.Append("document.getElementById(\"" + textBox.ClientID + "\").value = result;");
                sb.Append(Environment.NewLine);
                sb.Append("}");
                sb.Append(Environment.NewLine);

                sb.Append("function OnErrorOccurs(err)");
                sb.Append(Environment.NewLine);
                sb.Append("{");
                sb.Append(Environment.NewLine);
                sb.Append("window.status = err;");
                sb.Append(Environment.NewLine);
                sb.Append("}");
                sb.Append(Environment.NewLine);

                scriptManager.RegisterClientScriptBlock(base.GetType(), "CallBackScript", sb.ToString(), true);
                base.OnLoad(e);
            }
        }

        protected override void RenderContents(HtmlTextWriter writer)
        {
            EnsureChildControls();
            tbResult.RenderControl(writer);
            btnCall.RenderControl(writer);
        }

        protected string GetDateTime()
        {
            return DateTime.Now.ToString("MM/dd/yyyy");
        }

        Implement ICallbackEventHandler Members
    }
}

Okay, That's it, you can compile the project and deploy your WebPart to sharepoint site. I will give you the instructions about how to deploy a web part if you don't know that.

1. Copy compiled assembly to C:\Inetpub\wwwroot\wss\VirtualDirectories\

80\_app_bin, notice that 80 is the virtual directory related to your wss site, you can find the name from IIS MMC.

2. Modify the web.config file under C:\Inetpub\wwwroot\wss\VirtualDirectories\80 directory, add below line to SafeControls section:

<SafeControl Assembly="SPS2007.Research.WebParts, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null" Namespace="SPS2007.Research.WebParts" TypeName="*" />

You probably need to change Assembly and Namespace to accord with your assembly.

3. Execute IISRESET under command line.

4. Then go to Site Settings -> Web parts, click 【New】go to the New Web Parts page, find your web part, click 【Populate Gallery】, after that you can add your web part to a page when you edit a page.