Just found this article on a site from a Victorian college.
You don't have to get a steam cleaner....just boil the water in a jug or kettle, and pour some on the plant.

Did you know an effective and
safe way to eradicate weeds is
to steam or pickle them?

Steam them!
As a low tech weed control
method, pour boiling water over
any unwanted plants. The
hardiest weed will die instantly
when coming into contact with
hot water.
Many councils are now using this method with large
pressure steamers on the back
of trucks to immediately kill
neighbourhood weeds without
using expensive and hazardous
chemicals. You can buy steam
cleaners cheaply that can be
carried on the shoulder and a
quick run around the garden will soon eradicate those
unwanted plants. If you are a
good shot, you will not harm any
wanted ones.

Pickle them!
A 5-percent concentration of
vinegar is an effective weed killer
against annual and perennial
weeds such as dandelions,
foxtail and thistle. When applied
to the weed foliage, the acid in
the vinegar acts as a contact
herbicide that kills the plants but
does not persist in the soil or
cause water or other pollution.
For older perennial weeds, you
may need to apply vinegar more
than once. Try heating the
vinegar for added punch.