If you already have the .net framework 4 installed, you do not need it.
No harm in getting the one with it. If you need it, it will install it from that package.
EDIT
It looks to just have .net 4 support, I do not even think you NEED it. Chances are you already have .net 4 installed anyway.
You can check in the add/remove programs to see if you have it or not. It was released last year, so good chance you have it already.