Have you tried watching it using VLC?
Have you upgraded anything else (hw or sw wise)? Have you checked nVidia's community forums for similar incidents and possible solutions?
A couple 500GB hdds in RAID 0 is still 1TB. I'd say go ahead an get the 1.5TB, it's probably as cheap. Also, you do know that RAID 0 is just as horrible as one big disk...right?