While your machine has 8gb of RAM, the software may not need all of that. Usually the task manager is accurate. It can trick you by running multiple process of different names for sub processes, so keep the task manager up before you start vegas, then see which things load. Look for CPU and memory use.
Get the latest drivers for all of your hardware. Do not use windows 7 update to find these drivers, they are most likely older than what is on the manufacturers web site.