The plain "leJOS" is for RCX programming:
The story on why it is set to COM1 has to do with using 64-bit Windows 7 and the lack of a 64-bit driver for the RCX USB connection. Details are at a Windows forum: http://www.sevenforums.com/drivers/3445-lego-usb-tower.html
That section in Eclipse Preferences appeared by itself after I installed the RCX Eclipse plugin. Also automatically installed was an item in the top Eclipse menu for downloading the RCX firmware:
My enthusiasm in the Windows forum was based on the fact that the link shown above actually works. The serial RCX tower lights up, the RCX beeps, and the firmware downloads. Note that I had to set an environment variable RCXTTY=com1 instead of the usual RCXTTY=usb used in all 32-bit Windows systems.
I thought I was done configuring Eclipse for RCX but have since been disappointed when linking and downloading to the RCX:
That process works fine on my 32-bit Windows 7 netbook, but the error shown above appears whether the RCX is turned on or off, whether the Preferences choice is set to USB or COM1, and while the RCX is in exactly the same physical position that worked great for the firmware download.
I've run out of ideas on how to fix it and have resigned myself to just using my 32-bit Windows 7 netbook when I want to download to the RCX.