i usually see raids on avid setups.

You could just get a good quality hard drive
( the hard drive is the oldest technology in a computer,
and the average life is only 5 years ) and all it would do
is load/save your files a little faster.
Save your $$$ for a kick ass Video card like carrot juice said,
( just the wildcat would be more than enough-),
a dvd burner and as much of the fastest ram you can stuff in there.
avoid amd chips ( unless the mb you got is for them -if so sorry)
get the fastest processer(s) you can. when you render a 1000
fram raytraced animation you'll thank me.
I've rendered some high res stuff for print that takes all night for one frame.
and if you have any $$ left over, send it to me. I need a car.
just kidding
Joe