For questions regarding Photoshop Elements pleaase refer to the Photoshop Elements Forum.
If it helps, I have PSE8 and Photoshop CS6 on the same computer.
As R_Kelly says, they are completely seperate and, therefore, should run just the same, and independently of each other. However, I did have a slight issue, initially, in that I had to reset PSE8's scanner settings, in preferences, as, curiously, it lost connection to the default scanner after installing Photoshop CS6. Simply by selecting a different scanner option, then selecting the original scanner option again, cured this and I've had no further problems.