Nix - Cool suggestion, I plan on having custom cusors anyway, but I think you are right, a different cursor is needed when hovering over a button/menu.
My idea is to probably have icons very similar to the windows one anyway, (pointer, hand, resize, scale tools, etc) but have them feel more gamey and specific to my voxel style.
That reminds me, I need to look up how over games do modified cursors anyway, I guess most games stick with a simple solution, but there might be some legs in gaving cool animated or 3d cursors. (like the hand cursor from dungeon keeper
If I stick with the default windows cursors I will still probably switch to the hand for buttons, as because like you said, most people are more comfortable with that icon to mean "I am hovering over a clickable button"