We have a single solution which contains one webapp project and some accompanying projects. Our TFS 2010 is building this solution every night and deploys the webapp to an I
I have a similar situation where I have a TFSBuild.proj build file and I generate a handful of installers and packages at the end of the build, targetting each of the deployment environments: Development, Test, Staging, and Production. Properties defined in @Matt Shepherd's answer can also be provided directly to the MSBuild task instead of writing them into the individual project files.
$(OutDir)
In this case it is possible to specify the DeployIisAppPath and that value will be written to the deployment package parameters file.