Hi Marcin,
when you are talking abouts sensors, are you referring to the sensors plugin (lmsensors)?
those should be working, but i'll check on this issue and report any findings.
basically there is no guideline for now on how to develop those cgi, but you can see the rrdtool manual specifically
rrdtool data definition sections and include those onto the list of collectd-web
Regrads,
Kenny