you should know not to post a thread like this w/o posting your system specs. it's just plain OBVIOUS. we can't help you because 1. we don't know your problem, 2. we don't have your specs (which could be the issue). so we don't know if you have directx10 or sufficient RAM or cpu speed. so there you have it. dont post unless you tell us the specs
AMD Athlon64 X2 3800+ (o/d & performance rated at 4.14GHz) w/ HT Technology 1000MHz, 2GB DDR PC-3200, ATI RADEON™ HD2900 PRO 512MB GDDR4 512-BIT INTERFACE - WINDOWS VISTA ULTIMATE