Need advice on new build

At some point RAID 5 NAS's sold in store for some odd reason become more expensive than actually building a computer for it, so...
My new build will be used primarily for NAS and perhaps PVR at some point if I can ever get the recording to work.

I am planning to use CentOS, Fedora, Debian, or OpenSuSE for it.

I am stuck at the following decisions:

1: If I am using software RAID5 (my budget doesn't include a RAID 5/6 card, as I should have ample CPU power to spare with any modern CPU), it turns out that both intel and AMD has mobos that has onboard RAID 5. Since my CPU requirements aren't big (I don't exactly have anything older than a core i5, so core i3 or some AM3 athlon II will do as core i3's seems to be cheaper than a c2d at some point), Question is which one should perform better? (Should tom's put up an article about software raid performance like that?)

2: can anyone recommend me some tv tuner that fits the following?
1. new-ish (so I can buy it in a store)
2. analog-capable (it can be dual tuner or hybrid or analog-only)
3. work well with linux (mostly mythtv),
4. has onboard encoding (I am having problems to get framebuffer cards to work since the beginning)

I run raid 5 on my home system using an older 775 dual core. I've since ugraded to an extream quad. But I did not notice any speed incress with the change. I've also never noticed a load on the cpu due to the extra overhead. My raid 5 is 4 seagate baracudas 500gig. My trasfer speeds are about 300mbs a second when trasfering to a device that can recieve at that spead. I think software raid is fine unless you have a truly intensive work environment and are storing extreamly sensitive files.

I've been runing on the ICH10 southbridge with intel matrix raid for 2 years now. Not a single problem in that time. Been very very happy with it.

Got no guess on tv tuners for linux.