how do you ship a printer (still in box)?

Question

can you just wrap it up and take it to the post office?

Answer 1

Yes, you can just place the address in a location that is clearly visible to the post man, you can ship in the printer box.
You'll have to get it weighed to determine the proper postage amount, and they'll ask you the standard security question, as well as insurance needs on your shipped product.

However, you might want to check out Fed Ex and UPS ground only rates. They might be cheaper, and typically they can get it there in the same amount of time as the post office.