Conditional grey-out and disabling of cells

I need to find a way to do conditional formatting and disabling of a cell based on a value from another cell. For instance if A1=X,Y, or Z, then B1 will get grayed out and cell entry will be disabled. This is so that when skimming over the sheet, you can tell what cells in row B you need to put info in still, and if it's grayed you'll know you don't have to put anything there (and it won't let you). Didn't know if there was a way to do this. Any help is great, thanks!