Guitar hero 3 pc promblem?

today i gh3 for my computer everything i think has the minium requirments except for the ram i only have 1gig of ram on vista and its very laggy and im not sure if my graphic are good enough i have Nvidia 6150Se built in graphics can some one tell me whats wrong whys it laggy and my computer is a Hp Pavilion a6000n if you want to find the exact specs