The problem is those old 250GB HDDs are slower than new single 500GB platter HDDs like the Samsung F3 500 (same distance moved = twice the data read since the platter is twice as dense). Might as well get one good 500GB and skip the raid 0.
I also agree go 2*2GB RAM is a better idea than 4x1GB.
I have never heard of LC Power and have no idea what their quality is. Without a professional review showing good voltage regulation I wouldnt trust it. Corsair, Antec, Seasonic, PC Power & Cooling are brands with a history of reliability and that is what I try to stick with. Also get an 80+ certified PSU if possible. Bad power regulation and inconsitent efficiency will make your system have flakey performance and lockups and could even damage other components.
9800 GT is kind of old. If you could get a GT 250 or ATI 4850 for around the same price (or cheaper) it would probably be a better idea. I dont know what you are planning on using the computer for so its hard to know what graphics card would be best.
There is a suggest format for build advice in a sticky at the top of the forums. It would really help if you re-post in that format.