I have i7 machine with 8gb ram.
Tomorrow I will be getting the GTX 570 and and additional 8 GB.
I was thinking of adding a 4T raid 0 to the computer but was not sure if it will make much of a different.
I am currently using Sony Vegas and I am not sure what to expect from CS5 as far as hardware.

What kind of source footage are you working with?
What's your workflow?

Before you can decide if RAID0 would be helpful you need to determine exactly where your bottlenecks are.

If you are working with a compressed format such as MPEG or H.264 a RAID0 setup has no real value.

If you are working with uncompressed video then its an absolute requirement (unless you go to a proxy workflow).

Your average desktop hard drive can easily serve several streams of MPEG or H.264 without choking.

Windows has a performance monitor that will help you determine where your bottlenecks are located. Unless you are using very high bitrate video your drives won't be the bottleneck.

Thank you for taking the time.
Here is a link from Adobe TV that talks about raid and SSD
Maximizing CS5.5 Performance With Intel Xeon Processors - Maximizing Performance with Intel Solid State Drives | Adobe TV (http://tv.adobe.com/watch/maximizing-cs55-performance-with-intel-xeon-processors/maximizing-performance-with-intel-solid-state-drives/)

Hey Dror...

You'll find that most people use SSD's for their OS system at the current time..
When things improve, you might see a shift away from hard disks. But there's no mass migration yet.

But for the most part, people requiring Raid 0 are still using hard drives.