I'm currently in the process of applying SP3 + CU5 to all our SQL2005 Instances. I wanted to be able to quickly check whether the install was successful (we're experimenting with using SCCM to push to our standalone Instances).
Checking SQL was easy enough, just using @@version in a multi-query was enough. However SSIS is a little tougher, you can't check it via T-SQL and I don't have the patience to login to every machine and check it that way.
The solution I came up with uses SERVERPROPERTY('ProductVersion') to check the SQL build & [system.diagnostics.fileversioninfo]::GetVersionInfo() to check the Product version on the SSIS executable.
It returns a table with the Instance, Version, SQL & SSIS Builds and Notes (for example whether SSIS is installed & if installed do the SQL & SSIS Builds match). The code is here.