Here's the thing about taking a new baby to work: it's actually pretty easy ... at least, on the baby. Most newborns don't really care too much about where they are, as long as their basic needs are taken care of. And since you're not sending the baby to work alone, you're covered here.
(Now, taking the baby to work may not be easy for you, but this is a slightly different issue, and I'll tackle that another time.)
Newborns don't really do much besides sleep, eat, and go to the bathroom. Baby sleep is good; it lets you get work done. And eating is pretty easy, too, assuming you're breastfeeding and it's going well. Granted, you'll probably have to stay more or less in one place while you're doing it (though in a crisis or if you just really, really can't wait to get something from the printer, it is possible to walk around and nurse at the same time), and you may have to give up one arm for a few minutes, but generally this is not such a big deal.
But to change a diaper, you pretty much have to stop everything. And with infants, sometimes you have to stop everything NOW. (And a few times, you may have to stop everything, change the baby, and then change your own clothes--seriously, take an extra set of clothes to work and leave them there, just in case of baby explosions. And even one set may not be enough, especially for the baby. I had a couple days when I thought I might have to send an intern out on a Baby Gap run.)
In most cases, though, the question is simply, where are you going to change that diaper? And what are you then going to do with it?
Ideally, I suppose, you would change the baby in the bathroom (I think there's some set of "taking your baby to work" rules somewhere out there that insists on this, as a courtesy to co-workers, etc. etc., and that makes sense), but that assumes you have a bathroom big enough to change a baby in, which my office does not. Ideally, of course, your spacious office bathroom would also have a diaper-changing station in it--but I'm guessing there aren't too many of those out there, either.
There's always the floor, though with a tiny little baby this may feel a little precarious. (Plus there's the whole dignity factor, which may or may not matter to you.) If you can swing it, the best solution here is probably a port-a-crib with a diaper-changing attachment. True, this takes up a fair amount of space, but since it serves many functions, it's terrific if you have the room for it.
The diaper-changing thing on mine was sort of a little box with rigid sides and a flat, padded bottom. It cleaned up easily, put the baby up higher than she was in the bassinette attachment (I suppose you could also change a baby in the bassinette, except maybe in the case of the worst explosions, though since it's lower, it would be a little awkward and hard on the back; by the way, if you're getting a port-a-crib for the office, you definitely want one with the bassinette attachment), and was a nice place to store the nursing pillow when I wasn't using it. I forget what the weight limit was, but it worked until Working Baby was pretty big and solid and easy to put on the floor. (By the time the baby is crawling and scooting around, you're going to end up on the floor no matter what, dignity be damned. And, to tell the truth, this is the point at which many offices with official bring-baby-to-work policies make employees come up with other arrangements).
As to where to put the diaper after you've changed it, this one is a little harder. Maybe if you're in a big office with a daily cleaning service, you can just throw them in your trash, except for the stinkers. We have a once-a-month cleaning service (oh, how I love cleaning day and wish it came more often!) and otherwise take out the trash ourselves, which means it doesn't get done until absolutely necessary. (In a related note, dumping and/or digging in the wastebaskets is one of the Working Baby's least adorable activities, which is another reason not to put the dirty diapers there...)
When the diapers were smaller, I bundled them up pretty tightly, closed them up in ziploc sandwich bags, and threw them away at the end of the day in the garbage can out on the street. The really messy ones I ran out to throw away immediately. Not a perfect system, and there was more than one day I got to the street and realized I didn't have the diapers, and even a few days when I didn't realize I didn't have them, and then felt guilty all night after remembering, even though they were non-stinky diapers bundled up in baggies and so actually not all that disgusting, but still.
In the past three or four months, I've been alternating disposable diapers with gDiapers. (gDiapers are biodegradable, if you have a farm-sized compost pile going, and flushable. Also very cute, particularly in the new colors they just came out with. Also not particularly inexpensive, especially if you pay to have them shipped to you. But good for the planet--or at least the conscience, and can you really put a price tag on that?) The gDiapers are ok, and since our office toilet is pretty hardy, it mostly works to flush them, which helps with the "what to do with the diaper" problem, though the trade-off is spending a little extra time in the bathroom stirring up a bowl full of diaper sludge. Plus, one time we had a gDisaster, and that didn't make the downstairs neighbors very happy, and since then I've been a little wary of the gDiaper...
The disposables, I mostly dispose of right away outside, since it's summer.
Now, the big question is how to work potty-training into the day (and to fit a potty into our tiny bathroom)...