Looked on the forum and followed the suggestion to install to "Program Files" instead, so did as suggested and retried to use sencha command (cd into the senchatouch sdk).
This time got this error The system cannot find the path specified.
Have tried the sencha.bat files from within the senchatouch SDK (in command/bin and command) but no joy.
The only success I've had so far is using my local install of nodejs and using that to start the sencha.js file in the command directory in the senchatouch sdk (had to install findit, jasmine-node and uglify-js via npm).
Only then does it output "Sencha Command v2.0.0 for Sencha Touch 2" and show the help info.
Not sure if the actual command works (seeing as how it took me this far to get it to actually startup!!), but will give it a go.
BTW on my ubuntu linux, also been trying to get the sencha command to work. I've also had to the same procedure (but this time created an alias e.g. alias sencha='node /path/to/senchatouch2sdk/command/sencha.js')