You don't mention what version of Photoshop you are using so this may be somewhat different for you. In CS4, from Bridge select Tools>Photoshop>Load files into Photoshop layers.
If your version doesn't have that, you can download Dr. Brown's Services for your version and use "Stack-a-Matic". It also does this.
Here is the link to Russell Brown's site: http://www.russellbrown.com/tips_tech.html
I don't believe there is a keyboard shortcut for any of the above. I also don't believe that it is possible to do it directly from within ACR. I am sure someone will correct me if I'm wrong though.