I have a small but curious problem here. When I start PD, some objects from the iemguts library don't seem to load. However, if I find them in the help browser, they load properly there, and I can then place them on the canvas as usual. Has anyone else encountered this before?

Is it Pd-extended? Maybe you need to import the library before you put any objects in our patch...

I am running PD Extended. Think I worked out what the problem is: instead of typing [sendcanvas], I need to create [iemguts/sendcanvas], and it works first time. Funny that this should happen though.

This is one way of importing external libraries. You could also use [import iemguts] and then put any object of that library (maybe you have to save your patch with [import] and re-open it in order to work).

This is a newbie question, but I'm going to go ahead and ask it here. What does it mean to "import" a library? Clearly the iemguts library is already on my system, so why should it need imported? And surely I couldn't use this method to import an object that wasn't on my system?

Not sure about he details, what I know is that as of Pd-extended-0.43 there are certain libraries which are included in the core of Pd, but others that are considered external, which you have to import, cause your system "doesn't know" of their existence until you tell it about them (importing a library).
You can also use the start up flags to always import a library (if you're using it frequently). Go to preferences and in the Startup flags field, type "-lib /path/to/your/library". Should work...