Hi all! I've been browsing these forums for a while now and finally decided to roll my own. However, I can use some advise on the motherboard. To keep my options open in the future, I decided on socket 939 and pci-express. So far the nvidia chipset seems to be very well supported, so I kinda decided on nofrce4 as well. And as it will need to be (very) quiet, the chipset should be passively cooled. That left me with two motherboard options that both seem to be closely matched:

Gigabyte GA-K8N Ultra-9 (http://www.hardwarezone.com/articles/view.php?cid=6&id=1593)
Abit AN8 Ultra (http://www.abit-usa.com/products/mb/products.php?categories=1&model=278)

Any comments on either of the two (or others)?
I'm planning to start with modifying an old (fairly big) atx desktop case, with a cpu cooler (thermalright xp-120) sucking out the air through the top and an 120mm air intake on the left side. Therefor the abit OTES heatpipe might be less effective as the main airstream will go through the cooler up and out, not via the back. I could modify another board and switch the active heatsink cooler for a zalman one, but I rather not (unless there are good reasons of course). For a cpu I'm looking at a Venice 3000+, graphics will probably be a 6200TC.
Any feedback will be much appreciated!

If you're going to go with a 939 board with PCI Express you might consider the MSI K8N Neo4 Platinum. It is a 939 socket board with PCI Express and the NVidia chipset. It also happens to be part of Knoppmyth Reference Platform, so it's been tested pretty thoroughly. You'll need to mod the board just a bit for quiter cooling. The reference platform includes suggestions on a passive cooling system for the northbridge chipset and a quiter CPU fan.

You haven't really given us enough information to make a recommendation. You have already decided on the Socket 939 but haven't even told us if you plan to do HDTV or not, how many and what kind of capture cards, and if you plan to S/PDIF out or not.

I've had good success with both brands of motherboard (Gigabyte and ABIT), but if HDTV has a part to play in your future you'd be smart to include a Pentium platform in your search, as it still does a better job of decoding HD video. (And this coming from a lifelong AMD processor enthusiast.)

My production Myth box has an ABIT AS8 m/b with 3.0 GHz P4 with HT. It supports three high-def receiver cards (two HD3000 and one HD2000) and software playback of 1080i output with its nVidia 5200 card. I have three disks totalling 800G bytes in an LVM array for storage.

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Thanks for the info.
Indeed, I do plan on HDTV playback (only occasionally in the coming year) but I don't see recording HDTV happening anytime soon. So I'm looking at one capture card for starters and I think the PVR 250 is considered the best choice here. As for the reason for 939, I'm told the athlon64 are more power efficient which will make cooling easier and thus keep the case more quiet (especially with cool 'n quiet). I'm trying to get it (very near) completely silent with some undervolted Nexus fans. Also, the lower the power requirements, the better (in my opinion). And I think an athlon64 3000+ should be capable of decoding 1080i (right?).
I'll definitely take a look at the MSI board, seems like a good option with the chipset fan replaced.
By the way, very nice setup Liv2Cod! Now I'v got something to look up to

The newer Athlon 64s run remarkably cool compared to the competition. Right now my readings are sitting at 87.8F (31C) for the MB and 91.4F (33C) for the CPU, and the machine is very, very close to silent. Earlier in the day those tempratures were actually 3-4 degrees F cooler, and I've seen the CPU as low as 83F/28C early in the morning when the ambient in the house was around 60F. I'm using the Zalman 7000B-AlCu with the fanmate set on low, and have replaced the case fan with a three speed one that is also set on low. The BIOS is set to enable the cool and quiet support.

The MSI board looks nice! But I am a bit worried about the location of the nforce4 chip. That might become a problem with certain (maybe future) video cards and passive cooling as it is almost directly in line of the pci-e slot. I couldn't find the cooling solution the ref platform uses, but maybe they replaced the fan with a zalman chip heatsink. If so, then it wouldn't be as much of a problem.
Also, anybody tried to use that board with SATA yet? (I can get a sweet deal on a SATA drive).