You don't really need the special tool to install the plastic feet on the upper tensioners. I use a set of channel locks with summer rubber Robo-grip plier covers over the ends to prevent marring the plastic, but you can use the pliers with a rag, instead. FYI, if you are getting the kit with the upper tensioners, there's a lot more work involved to replace the upper tensioners as opposed to just replacing the upper tensioner feet. To replace the whole tensioner, you have to remove the rear timing cover, as well.
The other tool is the flywheel stopper, or ring gear tool, J-48761. This is made by Kent-Moore tools and saves a lot of work on the job. Once again, you can do the job without this special tool, but one would need to remove the upper plenum and both valve covers.
Here are a couple of links where you can buy the tool:
http://www.handsontools.com/Kent-Moore- ... 71450.html
http://www.etoolcart.com/nissan-ring-ge ... 48761.aspx
http://www.etoolpros.com/automotive-too ... 48761.html
Every once in a while you can find a used one for sale on Ebay or on one of the Frontier or Xterra forums.