Lots of ways you can do this, depends on your skills/budget.
Custom software?
I have previously written a pc .exe in director (yea a few years ago) that ran on a dual screen computer, laptop with extended display, where there was a controller screen with buttons that dynamically loaded jpg files in a folder onto each button and you could directly click on a button to switch to that image,
it also coped with video playback as well so you could click through a few slides and then run a video.
There was a section where some preset ‘slides’ had dynamic text fields – seem to remember raffle ticket numbers- so in the software you could type in the winning number and when you clicked the raffle ticket slide it came up with the bg image and winning numbers ontop.
Custom written took a couple of days to sort but dead simple to use – still runs weekly at a local sports venue 5 years on!
Web page?
Multiple ways of doing this- master and slave scenario is prob best with one pc running a web server, another one connected to it via LAN, have a page designed that auto refreshes every 30 seconds?
and amend the page from the remote computer.
depends on your html/programming skills as to how complex=nice you can make this both for the server displaying the content and the interface for updating it.
I’ve done this for several events and its stable and powerful as you can have the changes made from anything on the same network as the server – pc, iPad iPhone…
Dedicated software?
renewed vision Propresenter does ‘hot folder’ dynamic loading of images n videos i think, Think theres also a way to dynamically put text in – $400 or so.
resolume avenue -way over the top but does video playin and has some flash /quartz playback facilities you may be able to butcher to your needs….
sure there will be others as well,
plus as you say the hardware box way –
hire a kramer switcher and use the freeze function (other brands are available 🙂 )