I want to print from Photoshop CS4 onto a reasonably high-end photo printer. (Getting more colors is the motivation, not more speed.) Macs support this feature in current versions of their OS, even though they apparently don't run PS in 64-bit mode. Windows does not support 16-bit printing (without jumping through hoops) even though solid 64-bit operation of PS is supported.
The way your post was originally wriiten seemed to imply you wanted 16 Bit Printing as a 16 Bit OS (Windows 3.1 for example).
Once you start talking about Photoshop and decent high end photo printing -- that's a different problem comp[letely.
This now depends entirely on Photoshop and your Printer driver. In general if you set Photoshop to do the colour management and turn off any printer "Photo enhance feature" you should be able to get the maximum colour possible from your printer.
However it's not easy to set this up decently unless you have an extremely high quality monotor.
Here's a demo on 16 bit printing in Photoshop -- note it's NOT a Windows problem.