I recently came across a helpful post on Jim Morris' IDeveloper blog. He describes how to get your SSIS packages "building" in MSBuild (allowing them to be built by Team Build as well).

The problem stems from the fact that Team Build uses MSBuild but SSIS projects are not written in MSBuild format. They are just plain old xml. So did you get MSBuild in your SSIS or did you get SSIS in your MSBuild? Not sure why this (and other BI) project type was not written using the MSBuild schema... In the meantime here is a solution to get your SSIS packages "building".

Here's a link to Jim's post:
You got SSIS in my MSBuild