Create a new (empty) project with File | New | Project. Under Project | Project Properties open tab JDK Tools and Select Tool Type: Compiler. Check the MIDlet option. Now you are ready to successfully edit/compile a MIDlet.
In the menu bar choose Configure | Options. In the left pane click on Tools and then on the appearing button New. Select Program and choose java.exe that normally resides in c:\windows\system32.
In the left pane click on java. Adapt the checkboxes as shown below. The text field Arguments starts with -jar c:\jars\midpak.jar, then follows all arguments of MidPak as stated in the installation guide. Typically (all on one line, when using ProGuard and the Gidlet framework):
With the mouse anywhere in the menu bar, click right and select Tools. In the menu choose Configure | Customize, right-click on the appropriate tool icon and select Button Appearance. Adapt name and image as wanted. Drag the tool icon to a menu position you like.
After a MIDlet is edited/compiled click an the tool icon and MidPak should do its duty.
You may modify MidPak's arguments to your need, or just try the -d and -v options.