Patch 5 does NOT support Vista SP1. A hotfix must be installed on top of patch 5 to make it compatible with Vista SP1. This hotfix can only be requested by submitting a ticket through the corporate helpdesk, and having it escalated (be sure to tell the customer to reference KB 615037).
We estimate that patch 6 (containing the fully QA'd hotfix) will be released in July of 2008.
I want to reiterate, because the KB article is a little confusing, that we don't recommend upgrading and then installing the hotfix, that's only a temporary workaround until the patch is fully released. It is mainly intended for people who already had Vista SP1, and try to add VSE 8.5i to the system.
They may not have to escalate a ticket to get the hotfix, but they will need to call technical support regardless.