Others (Randal especially) are right about grid being a more suitable geometry manager. There is nothing to stop you from putting a frame inside a grid cell, and then using pack as the geometry manager for the frame.

I tend to use grid cells for columns that I want to line up, and frames with pack if a cell needs to contain multiple items that don't line up (with anything outside the cell).

As an example of getting the best out of grid, see the RPN calculator tutorial on the Tk wiki.