My relatively recent version of CS4 does not enable me to open CR2 raw files generated by a Canon 5D MKII. I was told that it should be able to open this type - just need to get the more recent version of Adobe Camera Raw installed. Where do I get this and how do I update?
You don't say whether you're using a PC or Mac.
These pages should give you what you need:
Generally speaking, you can get the update installed automatically through choice of Help - Updates... at the Photoshop menus, but the above pages also list manual installation instructions as well, I believe.