Lukeje said:
You should check this thread that gives the minimum requirements:
http://www.minecraftforum.net/viewtopic.php?f=35&t=29145
Edit: ...also note that just because a game has `low graphics' doesn't mean it can't be computationally demanding (I mean, have you seen the size of the gameworlds?!).
This.
Also, the game might have "low" graphics, but it has alot of effects (eg. breaking a cube releases a shower of dirt and stone and some materials)
But, you can help your computer cope with the size of the gameworlds by decreasing the range at which fog is dispelled.