The advice in ubuntu-linux-driver-for-huawei.htm proved very useful.
The steps did not exactly mirror the advice but on unzipping Linux.zip there is a readme which tells you to run the .install. After that simply plugging in the device invokes Movistar which, except it's in Spanish, looks rather like the interface one gets in XP).
1. Download the Huawei E173 driver for linux available here: http://frontlinesms.ning.com/forum/attachment/download?id=2052630%3AUploadedFile%3A51370
2. Unzip the linux.zip file in a convenient location, for instance on the desktop. Upon decompressing you'll have a new folder: ~/Desktop/Linux/
3. Right click on each individual file in the folder ~/Desktop/Linux/, chose >> Proprieties >> Permissions - read and write all + check on "Allow executing as a program"
4. Open a terminal window (e.g. CTRL+ALT+t) and write in command line:cd ~/Desktop/Linux/thensudo ./installand press Enter on all questions.
The Huawei E173 driver will install (the default installation path is in /usr/local/) together with a specific connection program called Moviestar 3.5G/Mobile Partner (program which we will ignore. If it pops up, you can close it with absolutely no problem).
5 - From this step on everything is simple and related to the installation of 3G broadband modems in general - the standard tutorial.
5.a - stick the modem in an usb port.
5.b. - This video (in Spanish) provides a demonstration.
5.c. - A new Device is found in Network Manager Applet. Click on it and choose connect.