A long time ago I knew what I was doing, and took care of tens of thousands of fish at a local pet store..
No longer
I second the "pay someone to do it" approach. Since this is for an office, you want stuff to look nice, not stink, and not cause a mess or be a huge time sinkhole. A novice starting a tank would not be a good deal.
Many companies do this sort of thing. Basically you pick out the tank size/shape and type (salt, reef, freshwater) a general idea of what fish, and they do the rest including weekly/bi-weekly maintenance. Call a local pet store (not a petsmart - a local store) for recommendations.
I wanted to do this too... Unfortunately our lease covenant precludes them specifically. Doh!