To keep the application from prompting the user to register, add the following registry key:
HKLM\Software\Corel\Corel\Paint Shop Pro\11\CorelReg\PR11
When running the pspxi.msi directly, it doesn't install snapfire by default. You can execute the MSI from the program files location with /qb to install.
There are a number of public properties that begin with "C_". Use these to control aspects of the install such as whether or not to install the Yahoo Toolbar and show the readme.
A Manual install will offer to download the extras if you register. This is a small download that can be repackaged and included if you want. I took these files and put them in the transform to install by default.