You could build a custom stat to see the BB amount from the previous hand, but custom stats aren't available in the trial.
If you're just starting out with PokerTracker you should definitely go straight for PT4 (unless you're a Mac user - the Mac version of PT4 isn't quite ready yet) as it is much more advanced and easy to use than PT3, and PT3 is no longer having new features developed.
PT4 Download Page
