Can I make tmux scroll from my trackpad?
The mode is referred to as "copy mode" and as long as you're running tmux 1.5 or higher you can add:

setw -g mode-mouse on


to your ~/.tmux.conf file and tmux will automatically enter and exit copy mode when you use the scroll wheel on your mouse.

As a bonus, this option allows you to select the tmux pane with your mouse:

set -g mouse-select-pane on