disable certain toolbar items when in a table

hi all,

i'd like to achieve the following two things:

(1) disable certain core toolbar buttons (e.g. <hr>) when the cursor is in the context of a table cell

(2) write a toolbar button plugin which is only active when the cursor is in the context of a able cell

i've asked this before, but didn't formulate it in such a clear manner ;) maybe i get lucky this time around ;)

cheerz in advance ... caillou