[Cryptography] How can I make use of the AES hardware on new CPUs?

[Bear]

I am writing some software for which I would like to take advantage 
of the built-in AES instructions supposedly now included in AMD64 
CPUs. So I have two questions.  

First, how do I get at them?  Do I have to insert conditional  
assembly code directly to use that, or is there a linkable 
library? Hopefully a reasonably portable one since I need to 
make both windows and Linux clients?

Second, is there a way to detect whether or not that hardware 
is present, so that I can create something that may run more 
slowly but at least doesn't crash horribly if run on an 
earlier CPU without an AES instruction built in?


Bear