I can't imagine how it would fail... High end of pot to the video
card, low end to ground, wiper to monitor/projector. Any failure there
would be rather unusual, to say the least.

I was thinking if you had it faded "up" and then accidentally shorted the
wiper you could blow the card, im unaware of the protection on VGA cards and
overly aware of the lack of care/knowledge of students when handling
hardware so I like to be extra specially sure it cant cause damage,
especially as it may end up being used with something other than a basic PC
etc, or even have a bored idiot pushing the end of a biro into it. I just
like to cover my back!

That said, I've not seen any VGA outputs that won't survive some abuse
such as shorts. They are not high current devices... I don't think an
additional amplifier is worth the effort, afterall it could be the
failure point!

Thats the kind of info I needed really, I know they arent high current
devices but I've blown a few low current devices in my time with stupid
mistakes and accidental shorts - the input device *could* be a custom-built
high-end machine and I dont want to be liable for replacing the card, but as
you say its not overly likely to fail. I'll knock one up at the weekend and
let you know how it goes on.

Cheers
J