Is there any way to change the local admin password using the group policy on a domain environment?

Unfortunately not. There are a few free third party applications that will do it. Here is a link toa VB script that will do the job.
http://articles.techrepublic.com.com/5100-10878_11-5198818.html

If you deploy Group Policy Preferences, this can be automated using GP as follows: http://www.windowsecurity.com/articles/Top5-Security-Settings-Group-Policy-Windows-Server-2008.html

The article references Windows Server 2008, but GPP can be deployed on a 2003 network so long as you have at least one Vista computer that you are managing Group Policy from, and so long as you have deployed the GPP Client-Side Extensions to your XP/2003 clients via WSUS or a similar mechanism.

After a lot of seraching there is no way to do this in windows 2003... i had to did it manually...

I disagree with the assessment that it cannot be done manually. The link I provided above to Group Policy Preferences would have accomplished with the OP was asking for in a 2003 environment.

LauraEHunterMVP :  If you don't have a Vista computer on your network its not exactly feasible is it? In a pure 2003 / XP situation a script would have been the best answer.

A script leaves the password embedded in clear-text, anyone with enough savvy to access the script would be able to access the password.  

Vista has been on the street for over a year and is into its 1st service pack, we're reaching the point where "requires at least 1 Vista box" can't be considered that onerous of a requirement anymore.

Well I do not have a Vista computer in my environment.. It's a pure Windows 2003 DC and 2000/XP clients environment.. So do you still think your solution can be implemented in this. I will be very thankful to you if you can tell me how to do that.

What is wrong with the script method? It works fine, and if you store it in a secure location no-one else can access it.

Thanks zzingalala.
Vee_Mod, notice I never said 'assume' about the secure network location. If you store the script in a folder on a server with file permissions set then it is in a secure location. The point is, is that in reality for the situation defined in the question, the answer should not be 'buy a copy of Vista'.