If there's an application that you want to automatically install on every computer in your Windows domain, read this article.
I'm currently in the process of implementing automated installation of LogMeIn remote access software on every workstation in the domain at a couple of client sites. One site uses Windows SBS 2003, which has its own way of assigning applications. The other site does not have SBS; just Windows Server 2003. At that site, I used the method described in the article referenced above and it worked perfectly.