Remember, if your computer barely meets the minumum system requirements, then yes, you will have problems. Minimum requirements are just there so you can install it, other than that it is strictly recommended to upgrade your computer. How much memory do you have in your PC? How about the processor speed, and video card?
My dad'* friends' PC runs flawlessly with Vista, but he is a gamer and has dual AMD processors, 4GB of ram, 2 SLI 768MB video cards, and 2 500GB SATA HDDs.