I woud like to suggest adding the superb adventure game "The Longest Journey" to the list, which is ridiculously easy to run. If you loved Grim Fandango and the Monkey Island series (which I did, of course) then you'll really enjoy TLJ. In fact, I might even say it's better than both in terms of story, dialogue, and puzzles (which are all balanced perfectly). It only falls short in terms of music and humor, at least in terms of comparison to GF and MI. It's sequel, "Dreamfall," is fairly graphically advanced, but it might just be stripped down enough to fit this list too.
Also for the adventure fan: "Loom," "Indiana Jones and the Fate of Atlantis," "Sam and Max Hit the Road" + "Sam and Max Season 1" (6 episodic sequels to "Hit the Road" with another season in the works) "Full Throttle," and "the Dig." (If any of those are missing, that is. I already saw DOTT there.)
I would also like to suggest adding "The Movies" + it's expansion, "The Movies: Stunts and Effects" from Fable's developer.
If your machine can run Fahrenheit, aka Indigo Prophecy in North America (which is an excellent, excellent game in it's own right and one of my all-time faves) then it should run the Movies just fine.
The Movies is a challenging but interesting strategy, sort of a mix between the Sims and Roller Coaster Tycoon series, but it's real strength is it's movie-making simulation, in which you can make your own digital films with literally few limits but your imagination and patience. It's expansion improves both aspects of gameplay and adds stunts to the films, played by your own stuntmen trained in the stunt training centers you buy. It's quite fun to see your rising stuntment stars abuse pyrotechnics, torture devices, etc. as training and then see it all come together in the filming of your latest project.
Also from Fable's developer is the excellent duology, Black and White 1+2. The second one is quite graphically enhanced (heavy use of pixel shading), so it might not be right for the list, but the first is a breeze to run.