If this is a modern office I'm making some assumptions:
With all your colleagues at one end of the room there'll be a bank of windows to one side of them, the overhead light will be flourescent.
That in itself is a lighting nightmare, the people at one end will be lit with quite bright daylight and at the other with just flourescent. The colours and intensities will vary on every one of them.
The first question is 'how many of them are there?'
The 2nd question is 'Is there an alternative location?'
3rd and 4th 'How many flashguns and do you have a method for firing them off camera?'
Some thoughts; If you can get them all at one side of the table facing the windows and turn the lights off, see how much light you've got and if you need to supplement it with flash at least the amount of daylight will be uniform, and if you have to add flash, at least all the light will be a similar colour.
Getting them behind a desk also adds some interest (people standing in line against a wall is very boring / ugly), and you can shrink the width and add interest by standing some behind.
Bouncing the flash off the ceiling will help with softening, not having them against the wall will help reduce ugly flash shadows.
Watch out for gaps between them, it'll be more difficult getting colleagues bodies to overlap than it is families, and gaps between people ruin the look of shots.
Test the set-up and lighting out beforehand with a couple of colleagues and then you'll have the confidence required to pose them all in an instant as soon as they are all together. This is the most important bit btw.
