Unfortunately, Spiderplant no longer sells these units (though they were kind enough to replace ours when it died recently), and in fact, no longer exists as an enterprise. Similar equipment can be purchased though through Dallas Semiconductor's iButton site.
Spiderplant's "therm" software works well. We wrote a simple script to record the temperature of each sensor every 5 minutes using "therm", and to trim the log to keep only the last 7 days of data. Weve created a simple CGI/Perl web interface to view these temperature logs.
The Hot Little Therm is located 20 feet from the Sun workstation; a longer serial "phone" cable would increase this distance. The therm sensors are about 10 feet long and radiate from the Hot Little Therm (the sensors can also be daisy-chained to a total length of about 300ft.).