Converting latitude and longitude to state plane feet

1. Access the "Project tool"

Click the Arc Toolbox window icon which looks like a small box with a red really-that's-supposed-to-be-a-toolbox icon in the center (for me, it's
directly under the "Customize" menu header, but that will depend on where you root your menus)

2. In the resulting Toolbox window, click Data Management Tools, then Projections and Transformations, then Feature, then Project (double click).

3. Select your input dataset, re-name your output dataset, and choose your output coordinate system

For example, I was projecting file Cases_2002, so I renamed my output
dataset "Cases_2002_proj" and chose "Predefined coordinate system", "Projected
coordinate systems", "State plane", "NAD 1983 (US Feet)", and my state of interest.prj file.

This adds the newly projected layer to your mxd file.

4. Next, open the attribute table of this projected layer, add a field type "Double" and name it "X_St_Pl_ft".

5. Right click the X_St_Pl_ft column and choose "Calculate Geometry".

Sometimes, I randomly encounter an error that I cannot utilize this function unless I'm in editor mode, even if I am in editor mode (enter editor mode by right clicking layer, selecting "Edit" then "Start editing"). When this happens, I save my project, shut it down, and restart ArcGIS 10, which fixes the problem.

6. Select Property: "X Coordinate of Point" and "Use coordinate system of the data source". Select Units: "Feet US [ft]"

7. Repeat for State Plane Y coordinate.

NOTE that if you performed a join on the original layer, the join may not transfer to the projected layer.