upgrading trashed my font display

[Adam Hardy <adam.ant@cyberspaceroad.com>]

I upgraded a whole set of packages in etch using synaptic.

I answered several of the questions posed by the installation processses of some 
of the packages but I must have answered one of them very wrongly.

Now my system-, firefox- and thunderbird text refuses to appear until I drag the 
mouse across it.

I am not sure how I managed to trash the system and I don't see anything 
immediate to restore it.

This is the same in KDE, Gnome and Enlightenment. Can someone tell me where to 
start?

Thanks
Adam