As a developer, one of the first things I did to my notebook (running Vista) is disable the UAC - I can't stand it - it keeps me from installing things like Virtual Server (which is not supported on Vista - but works perfectly fine), and is basically something I'm not worried about.
Until I want to add a printer that is a network resource on my LAN. I get the error that the printer cannot be added - "The specified print monitor is unknown."
Very informative - I know.
Well, believe it or not - this occurred because I set the value for the UAC to zero - or basically disabled it. The issue pops up because the network printer resource MUST install a driver on your local workstation - and if UAC is turned off, by default - MSFT has written into this - DO NOT install any foreign device - period.
To resolve - I open the registry HKLM\Software\Microsoft\Windows\CurrentVersion\Policies\System and set EnableLUA to a value of ONE "1" - reboot - and the printer adds just fine.
The question I'm sure you're asking yourself... "Do I have to leave UAC enabled???" - NO NO NO - and that's the nice part.
So, re-enable UAC - add the printer - disable UAC - and enjoy.
Hopefully this helps some other unsuspecting Vista lover...