This is pure speculation, as I refuse to let Real Player anywhere near my PCs ....
If there is a background timer / process that is counting down until the next interval that Real has decided to show the 'Update now?' popup, that can be stealing your CPU cycles.
Alternatively, Real may be loading a background program, ready to 'spring into action' when you click one of the Real icons, that is impairing the performance of your graphics card drivers.
To test, go to start > run, type 'msconfig' (without quotes), click the Startup tab and untick anything associated with Real.
Restart, see if that helps.
Incidentally, there is a free alternative to Real Player that is not nearly so intrusive. See click here