as per title...

basically want to be able to show progress on a gantt chart...
so lets say you have a job that you plan to take from 01.09.06 'till 14.09.06
you also want to see progress over this time period to monitor if it's on
track or not
so I would see this being able to be displayed by filling a merged cell
(that spanned the desired time period) the more progress made the more of the
cell would be filled in.

as per that scenario... on about 07.09.06 the cell would be half filled
showing you was dead on track.

or maybe there's another way to do the same thing

I will doctor a jpeg to show what I mean (see below)
You see tasks number 1, 2 and 3 span dates from 1.9.06 till 10.9.06 so take
up the same amount of space on the gantt chart but they are at differant
stages of completion so the cells reflect this in the amount they are filled.
http://img145.imageshack.us/img145/97/cellsru3.jpg