Upgrade Panther's Calculator:

From Macworld:

Add New Calculator Modes

Do you miss OS 9's Graphing Calculator? Well, you can bring it back to life in OS X 10.3 -- along with an expression input sheet and a hexadecimal calculator.

First, open the Applications folder and create a duplicate of the default Calculator application (this gives you a backup in case something goes wrong). Control-click on your duplicate Calculator and select Show Package Contents from the contextual menu. In the resulting Finder window, select the column-view mode (View: As Columns), and then go to Contents: Resources. From the Resources folder, drag the Graphing-2D.calcview, ExpressionSheet.calcview, and Hexadecimal.calcview folders into the PlugIns folder in the previous column

Launch your duplicate Calculator application. You should see three new options listed under the View menu: Expression Sheet, Graphing, and Hexadecimal. -- rg