Hello Jon, thanks for your help. Ok, one thing at a time. I installed the "gprs" sub directory in "the tessel-code" sub directory as per the tessel site intro. Then I changed into this directory and typed the line "npm install gprs-sim900" as per the instructions.
that is: c:\program files\nodejs\tessel-code\gprs\npm install gprs-sim900
I attach a screen shot of the error messages. The gprs module appears not to be installed. I then went back to the "nodejs" sub directory and tried the install command there, but no success. The tessel module is working ok as stated before, because I can access my dlink router with wifi and change the blinky.js file around to get all the leds to flash. I have developed my own microcontroller boards for years and I wanted to connect them to the web and or mobile phones for new applications and this seemed the most straight forward way. All the very best John
PS I live in Switzerland, so time zones may affect us.