Start the IAR Embedded Workbench from windows (2000,xp, probably even 98
will work).

Ensure that he cable is plugged in the parallel port.

Choose "Create New Project in Current Workspace"

Choose ASM only project.

Choose where you want this project to reside on disk, use whatever name
you want.

This will create a simple project that has a sample asm file in it.
(asm.s43)

Once you have the workspace look in the left panel and right click on
the workspace name you
created. Click on options.

Choose General category, Target tab: Ensure that the correct device is
chosen "msp430f1121a". ["mps430f1232" for the ATS3B]
Click on the box to choose "Assembler only project".

Choose Linker category, Processing tab: Ensure that the "Fill unused
code memory" box is checked.
Should be filled with 0xFF.

Choose Debugger category, Make the driver "FET Debugger"

Choose FET debugger category, click the box "Verify download".
Ensure that the Connection is LPT1: (or whatever your parallel port is
named)

Right click on the asm.s43 file in the left panel and remove it.

Click the X in the right panel to delete the edit for asm.43

Copy the firmware that you want to download to the same directory that
you just created this project.

Right click on the project in the left panel and "add files".

Click on the filter to see the assembler files (*.s43) and choose the
file you want to load.

Double click on the file you just added to the project to see it in the
edit (right) panel.

Press F7 to compile it.

If you have an ATS-2 turn it on before connect the cable/wires, doesn't
matter for the ATS-3, i.e. you can turn the ATS-3 on after you connect the 
cable. Either rig must be powered up for the download to work.

Connect the cable/wire to the rig.

Press Ctrl-D to start debug. This is actually what does the downloading.

Press Run (from the debug buttons that just came up), then exit debug.
Your rig should be programmed with the new firmware and running.