I agree for the most part, but it depends what type of video capture you have. If your capturing through firewire an ATA-33 hard drive is fast enough to capture without loosing frames. But if your capturing from almost anything else I would have to suggest raid-0.
I have a raid-0 array for video capture and games and it gives a huge performance boost, even while editing video in premiere its faster over a single hard drive. The only bad thing is your drive can suddenly get a bad stripe and then your entire array is lost and you have to build it again which is what happened to me recently. I lost tons of footage I had captured and ALL of my games and saved games. Now to remedy the problem I got a 60 gig 5400 rpm hard drive to back up data too (for $50 at bestbuy it was a good deal)
And what he means by software raid is that NT kernel Operating systems (I think NT4, Win2kpro, and XP pro) will take two hard drives and to software raid without a special raid controller. This method is faster than one hard drive, but a fraction slower than hardware raid. For the most part I believe that 8mb cache will help when you do things with smaller files and maybe some games, but isn't really much help with large file video manipulation and capture. I'm sure its a slight performance boost but not much.