I can't give any advice about your 'gadget', because I don't know what
variety you're using.
But as for Google Charts, those charts are merely images that render
according to the GET data appended to their source addresses. The
images themselves don't do any retrieving of data, but rather they
must have all data supplied to them upon request. To use Google Charts
with a database, you must build an intermediary layer that reads from
that database and constructs the chart's URL.
All of this information is available at
http://code.google.com/apis/chart/.