I can't believe that person sold their old computer with iwork 09 and office 08, and the mouse and case, but good for you. (unless they didn't want the mouse and case anymore). Put the "old" (but still current version) software on your new shiny toy and you're good to go.
you lose applecare though, but it will net you more for the machine.
Of course, you have to slick the hard drive and re-install Leopard, or better yet buy another hard drive off newegg and did a fresh install on that. (Given enough time and effort, someone can probably get any data that ever existed on a hard drive off of it.) And at least be fair to them and include the Leopard install disc too. (LOTS of used and older apple computers from 2001+ or so on ebay don't include OS X install discs, but have it pre-installed, disappointing actually)
Many times I wish there was a site for computers like Kelley Blue Book or edmunds.com is for cars. (you put in a bunch of information about the machine you want to buy or sell and it tells you what you can expect to get or pay for it, constantly updated of course)