Since that test file opens in Firefox when run directly but opens in IE when run from within UR (and other URLs opened from UR also open in IE), there is apparently something different about the Ultra Recall process environment/configuration that is resulting in the different behavior (as I mentioned, it works as expected in our tests on Vista Ultimate, but I haven't tried Vista Home Premium, so it could be something specific to that version of Vista or something funky about your configuration).
Is UR being "run as administrator" (on Vista, even admin users don't run as admin ["elevated" in Vista parlance] by default), or is there any software installed that might somehow be affecting what a
ShellExecute call does for a given process?