1. Download the Rocket zip file from www.rocketcad.com.

2. Unzip the file, maintaining the directory structure. The simplest install is to put it in C:\, but you can put it wherever you like, including on a network drive.
This will give you the directories C:\Rocket, C:\Rocket\Lisp, C:\Rocket\Lisp, C:\Rocket\Blocks, C:\Rocket\Terminals, and C:\Rocket\Spreadsheets, each containing a number of files.

3. Start Autocad. Open the Options dialog box either by selecting Options under the File menu or by entering Options at the command prompt.

4. Go to the Profiles tab, make a new profile and call it Rocket. Make it current. (You can ignore this if you're adding Rocket to an existing profile.)

5. Under the Files tab, double-click on Support File Search Path. Click the Add button, and add the directories created in step 2, in that order: C:\Rocket, C:\Rocket\Lisp, C:\Rocket\Blocks, and C:\Rocket\Terminals. (The Spreadsheets directory doesn't have to be pathed.) The Browse button is good for this.
Use the Move Up button to place the new directories to the top of the list. (This will ensure that the files in these directories are used and any other copies are ignored.)

6. Press the OK button down at the bottom to save the changes, and restart Autocad.

7. Enter the Menuload command at the command line. Beside the lower box titled File Name click on Browse and a new box will appear.
Down at the bottom change Files of Type to "Legacy Menu Template (*.mnu).
Go to C:\Rocket, highlight Rocket.mnu and press the Open button.
Now you should be back in the previous dialog. Press Load and Close.
That should do it.

Troubleshooting.
If something doesn't function correctly it is probably because AutoCAD can't find a file it needs, or has an old or incorrect copy.
The command (findfile "filename.ext") can be used to see which file autocad is using.
Enter the text, including the brackets, at the command line, substituting the name of the file you are looking for for filename.ext.
Autocad will return the path to the copy of the file it is using, or nil if it can't find one.
The major configuration files which Rocketcad uses are Acad2.lsp, Acaddoc.lsp, Acad.pgp, Acad.lin, and Electric.slb.
The copies used by Rocketcad should all be located in the C:\Rocket directory.
The menu file can be checked using the Menu command. You should be using C:\Rocket\Rocket.mnu.
If this is not the case it is typically best to check your directories and the settings under the Files tab in the Preferences dialog box.