my question is i have a acer aspire laptop i just but command and conquer 3 it plays but slow now if i change the hardrive to a biger one and more memory would that help out the graphic card that i have is ati
Hard drives only affects load and save times. It will not increase frame rates.
More system memory can help depending on how much you currently have, however it will be at best incremental. For example if you upgrade from 1GB to 2GB you may see something like a 3% - 5% increase in performance at best.
Your only options short of buying a new, more powerful laptop is to lower graphics quality and/or resolution.