I have a 2007 honda CRV. I was looking into engine block warmers ( http://honda-parts-and-accessories.stores.yahoo.net/genhoncrvenb.html )
And I was wondering how easy something like this is to install.

There are different ones available. The ones that slide down into the oil dipdstick and the ones that attach in line to the lower radiator hose are the simlpest.

There is another that replaces the knock out freeze plug on the engine. Those are the most difficult.

The ad in your link really is vague. Try Auto-zone or Advanced Auto. I know they used to have them. Most deisel engines require some type of block heat to make the engine easier to start. (In colder climates)

depends on your mechanical abilities and tools that you possess. Right? Easy if you got the tools and are not freaked out when you open the hood.

There should be a few different ones available. The first one is a magnetic one that you just attach to the bottom of the oil pan granted that the pan is made of iron. If it is aluminum, that won't work. The other way that I know of is in the way of a engine block heater that replaces the dipstick with an electrical cord on it. You just unplug it before you set out each morning and plug it in at night.

I'd let the dealer do it. I had one done for a Mazda I once owned & it only cost me about $110. Right now, my 07 Impala came from the factory w/ one. Since I was ordering the car anyway, what's another $50 on a $25K car?