I think that the + - buttons disappeared recently (with the release of live6?)... they were used to zoom in/out on your sample, which you now do by left-clicking on the sample itself, and (still holding the click), moving up or down with the mouse...
I think that's it, but I cannot check this coz I don't have live5 installed anymore...
but anyway, I have live6, and I don't have the + - buttons either!