so the conclusion is. we should not upgrade to vista in next 3 years, or never think about it until windows XP is dead, anyway we can install one or two client for test purpose.

Vista has released for more than one year. and the service pack 1 has out for one month too.
windows XP is a very successful Operating system. it runs perfect in enterprise environment.
Microsoft seems very eager to push users to upgrade the os from xp to vista, its ok. and microsoft also released a special tool for easy deployment. Microsoft Deployment Toolkit 2008: http://go.microsoft.com/fwlink/?LinkId=103947
its possible to deploy vista and office 2007 using this toolkit so that we don't need to install office to client computers by create a office install group policy in windows 2003.

this is good news. now deploy vista is as easy as deploy xp.

Can we deploy?
1. There is a major problem, the 3rd part software compatibility. i run vista on my home computer for 6 months without compatibility problem. but i believe business software is not in this case. they provide new edition very slowly. at least we have to test all of them for a long period.
2. another problem is cost.
it cost lot of money for upgrading xp to vista, if not? we have to maintain 2 kind of client operating system. xp and vista. this increase maintenance complexity.

can windows xp full fill the needs?
not many people complain and all software running on xp are stable, maybe vista can increase a little bit stability and security. not worth us doing so.