You have nothing to worry about. Your system has assigned 512MB of memory to your on-board GPU (as a result of the auto setting). Since it is reserved for the GPU, it is not available to Win7 for other uses.
If you are going to continue to use your on-board GPU, you can change the amount of memory assigned in the BIOS, but you really don't need to. 512MB is a good size for most applications.
If you ever install a discrete, stand-alone GPU, the on-board GPU will be disabled and the memory will be available to the operating system.
Bottom line, you are good to go with nothing to worry about. Good luck!