Mouseover-triggered text commentary nodes
This is a bit of a weird project 
I'm developing an addition to the Digital Game Museum's Evolution of the Controller exhibit. We've gotten ahold of a Novint Falcon and we want to build a small, moderately simple level within Portal 2 that shows off the controller.
However, we can't guarantee that players will know how the controller works. In fact we can't even guarantee that players will know how the portal mechanic works. I've decided to horribly break immersion by putting hints and guides throughout the level for the sake of the exhibit.
I'd like to place some reasonably obvious commentary nodes throughout the level that display text onscreen when the mouse cursor rolls over them. point_commentary_node seems ideally suited for this, but I'm not experienced with Hammer and I'm not sure how to rig up the "display text on rollover" deal. Bonus points if I can rig things up to display images instead of text!
Suggestions? If I'm given a few simple descriptive steps ("place entity, edit this property, write this script, add this function") I can probably puzzle things out myself, but I simply don't know where to start.
Also, note that this isn't a normal commentary system - it should be enabled at all times, just as part of the level. The only thing I want to re-use the commentary nodes for is their model.
Thanks for any help!
You could use the entity Env_instructor_hint that displays hint messages of what button to use to achieve different moves, grab things, use portals etc. as an instructor. It's used at the beginning of the game, in first levels.
useful tools and stuff here on TWP 
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Yeah, like josepezdj said, an env_instructor_hint works best for this.
Also, if you're doing a demonstration/showcase kind of map, I would personally use the overgrown theme, as it is mainly meant to leave a big impact on the player. Plus it's very pretty.
Hmmmm, while it's true it's really pretty and atractive above many of the rest themes, I don't think it's very recommended for someone that has not much hammer experience since it requires a lot of detailing and knowledge imho 
Clean theme would work better instead, moreover taking into account the purpose of this project, merely instructive.
useful tools and stuff here on TWP [spoiler]
[/spoiler]Hmmmm, while it's true it's really pretty and atractive above many of the rest themes, I don't think it's very recommended for someone that has not much hammer experience since it requires a lot of detailing and knowledge imho Clean theme would work better instead, moreover taking into account the purpose of this project, merely instructive.
That is true, it's not exactly the style that a first time map maker would go for. (Well, not usually anyway, there are a few exceptions 
).
Of course, if OP was actually a really good mapper, then overgrown would be pretty neat. But yeah, for instructive purposes I guess clean style is better.
You could commission someone like HMW who's known for making Destroyed-theme maps to style it for you.
This looks like exactly what I'm looking for. I'll see if I can get it working in a few days (life is busy).
Clean theme would work better instead, moreover taking into account the purpose of this project, merely instructive.Yeah, Clean is what I'm using, for a few reasons. One reason is that it won't distract - we're not really showing off Portal 2, we're showing off the Novint Falcon through careful use of Portal 2. Overgrown is absolutely beautiful but it's just more visual clutter than we're looking for.
Conveniently, it also fits in perfectly with our exhibit's visual style, which revolves heavily around clean white backdrops and tables. Admittedly in our case we make those out of tarps and tablecloths, not out of overengineered robotic panels, but
Many thanks to everyone for the help, I'll post again when I've had time to rig everything together.