If you are the wheelchair user:
-Unless someone at work really dislikes you, your colleagues would most likely give you the space you need to move around. However, this doesn't give you the license to be president of the universe (unless YOU are the CEO) and demand that all work situations accommodate you.
-Be pleasant and acknowledge the little favors everyone does for you. If you're male, it would be nice to let the women go ahead of you. You may even open doors for them. Saying "please" and "thank you" always get you further.
-Sometimes, you colleagues could have the tendency to fuss over you a little too much, especially when they know you're not feeling well, or if they see that you have to deal with a tough load. It is perfectly fine to politely refuse their help when you're sure that you don't need any. On the flip side, offer them help when you can.
If you have a colleague in a wheelchair:
-You are never obliged to be nice. However, as a person, you are expected to be respectful. It would be helpful for you and everyone else to develop your peripheral vision. A lot of accidents could be avoided.
-Saying that you're sorry when necessary will also get you a long way. Offer help whenever you can, and I'm sure that your disabled colleague will lend you a hand in turn. You might even end up being good friends!