As to drives, you can't go wrong with the Barracudas per the earlier post. I'll qualify this below. You mention two interesting things - video work and backup pain. So you need fast disk i/o and a good backup solution (once again supporting my rant that high end consumer mobo's should be built more like low end servers)
Based on the MSI page, your K8N Neo4 has 4 SATA ports, 2 on the nVida chipset and 2 off of a Silicon Image chip. Both claim to run SATA at 300mB/s. That is VERY fast.
Ill Informed Side Rant: While I believe this is true somewhere on the interface, I don't believe consumer mobo's are up to it in their support chipsets. Nothing close to that speed is going to pump through. Besides, you'd need rock solid drives at the top end of SCSI320 to breathe that kind of air, and I don't really see that happening now even though there are a few new products out. However, if I was a VC this is one place I'd be investing... for next year.
'Cudas run at SATA150 plus bursts, which is still way fast, you can't beat the price point and they are available in all sizes. Personally I would not want to cross RAID technologies (SI and nVida) to get 4 disks. Start out with one or the other and 2 drives. Consider RAID 0 (10% read speed gain but increased chance of data loss since both drives will be striped across one another) or RAID 1+0 (aka 10) with one drive fully mirroring the other. To me, 1+0, RAID 5 or 6 only makes full sense if you have a RAID controller with battery power and the ability to take the mirror offline for backup and reinstantiate it later. You can do this, but only with a "real" RAID card... Promise if you're poor like me, 3Ware of you have a spare $600-800. So live on the edge and run RAID 0 with 16k stripes (for lots of big files consider larger stripes). To boot from your array, be sure to set RAID (or some such) right after CD-ROM).
As to backups, you could put a third drive on IDE and write a funky backup script to save specific stuff. If you hate swapping CD's, you might consider DVD-ROM. You may also be able to find a DAT3 device with IDE. Personally I use a small DAT3 autochanger I got from eBay for $80 with new tapes. I use Bacula, way cool open source at http://www.bacula.org/ .