I have characters that sit on a chair, type at a keyboard and speak to the player - though I had to make them up myself from an amended deafult character using Fragmotion and Milkshape.
I found that none of the default animations were set up correctly for positioning of a sitting player at the desk I needed them to sit at so had no choice but to make one sit correctly on a specific chair and at the right height etc.
Its relatively easy to do this if you have those modelling progs.
If not I guess the animations referred to by others might work though how you would get them in a correct pose I dont know unless you knew the exact animation frame numbers required in which case you would need some kind of modelling prog to view them in I guess. In that case you may be able to set up a sitting character more precisely for your needs relatively easily in your modeller.
A default sitting character animation would be helpful to many I would think.
