Photoshop :: Creating Crisp 32x32 Pixel Buttons

How do you create crisp buttons? I have a client that needs a number of buttons saved at 32x32, 24x24 and 16x16 pixels. I have designed the buttons in Illustrator, but when they are placed into photoshop they can end up blurring. I understand they have to pixelate, but the problem I am having is that some of the vertical and horizontal lines end up sitting between to rows of pixels and so spread across both, blurring the line. Is there any magic way to fix this other than fine tuning the position, or altering the vector? Or should these types of buttons be created in a different program?

I am generally very proficient with Photoshop, but I've never had to work at this scale before.