I have had multiple questions on how to enumerate SQL instances in your complete environment to run maintenance operations from a centralized environment. There are multiple tools which implement one of the methods or a variation of the methods described in the blog post below.

I keep referring people to this blog post. So, I thought I would put a referral of the same on my blog so that I can find it easily the next time.

Jonathan Sayce [Blog] has shown in his blog post what are the different methods to achieve this.

http://sqlblogcasts.com/blogs/jonsayce/archive/2008/02/10/programatically-listing-sql-servers.aspx