Vista - ClickOnce Deployment

Hoping there might be some in here who have experience with ClickOnce and
may be able to provide some guidance? We're using Visual Studio 2008 (SP1)
here.

We have a WinForm application which we deploy to the end user via a standard
Visual Studio Setup Project, but we'd like to switch over to ClickOnce to
take advantage of the supposed ease of deployment advantages -- it can be
deployed from a central location, the application can check for and install
its own updates, etc. However, we are running into a couple of issues....

If your application is already out there (installed on the client machines)
and knows nothing of ClickOnce, is there a best or most appropriate way to
convert over from a Setup Project based deployment to a ClickOnce
deployment?

The other, and more imposing issue is that of the seeming limitation of
ClickOnce in regards to a single-user and multi-user delpoyment. Reading
this article (http://www.code-magazine.com/Article...uickid=0902031), it
discusses this issue under point #2, along with several other limitations of
ClickOnce. Additionally, I found a couple other articles that break down the
differences between ClickOnce and Windows Installer:
http://tinyurl.com/lo882c and http://tinyurl.com/nktb2m. It seems that if
you have a single machine with multiple users, *each* user has to download
and install the application, which means you can have multiple copies of the
same application on one machine, and the auto update portion of ClickOnce
will only update a single instance, not all.

Is there a way to have a *single* application on the machine which multiple
users of the machine (aka Windows Accounts) all share, can take advantage of
the ease of install and updates the ClickOnce offers, but have the
versatility and control during install like the Windows Installer?

-- Andrew