I can think of a couple options:

1) Install SQL Server 2008 client tools, setup a folder and register your servers, then use the multi-script option to open a connection to all instances and run your query.

2) Install SQL Server 2005/2008 client tools and use SQLCMD and a script file to loop through all servers and run the query.

3) Install Windows Powershell and use a powershell script to loop through all instances and run the query (using SQLCMD or OSQL).

4) Use wscript/cscript and SMO

5) Look at Redgate tools - they have one that allows for running queries on multiple instances.

6) Other tools like the Redgate tools that allow multi-select queries.

7) Install SQL Server 2005/2008 and use SSIS to build a package that loops through all instances. This is more of an ETL tool though - but can work very well.

8) Use DTS to build a package

There are probably more - but I think that will get you started. Which one you choose will really depend on how often this needs to be done and whether or not it needs to be automated.