AMD fanboy here! Haven't gotten to the X6 just yet (next hardware upgrade), but the Phenom II X4 (the 65 watt chip) has been glorious. The performance is nigh onto perfect, and from a cost standpoint, you can build up to 3 quad core AMD systems for rendernodes for the price of one i7 chip (unless you go with the cheapy one....which pretty much defeats the purpose of -having- an i7, as the general clock speed is far lower).

From the standpoint of uber system vs distributed rendering, it depends. If you are doing -massive- (like poster sized) stills, or highly detailed stills, then it can be a coin toss as to wether a render network is worthwhile. If you plan on animating, then build the rendergarden, no two questions, and make your plans so that you can expand it with minimal fuss.

While you -can- use mixed OS's  with the Rendercow and rendernodes (at least with the higher end Vue packages; check and see which is the lowest one that does this) you will start to run into bottleneck issues.  And if you are going to have your main system as a 64 bit, then go ahead and make sure your render boxes are also 64 bit. This will make things more stable. Also keep in mind that the closer your renderboxes are in basic stats to your main box, the less likely you will be to run into the problem of the renderbox having to hit the swapfile hard, as the main box has 8 gig of ram and it only has 4, and the scene exceeds that 4 gig size. It works just fine...but you lose some efficiency when the rendercow has to keep writing to, and accessing, the swapfile, as HDD access times are the current major bottleneck in computer performance.

A KVM switch is cool; but you won't find one that does dual monitor switching, nor do you need it. If the renderboxes are dedicated to just that, you will only need quick access to turn them on and off, or restart a crashed rendercow or node. If you think you will want more than 4 nodes, go online and you will find 8 and 16 port KVM rackmount capable switches for a reasonable amount. There are also software alternatives, like remote desktop, WinVNC, and several more that allow you to remote access other computers. Another little trick is using WLAN, or Wake on LAN.....which basically is making sure your motherboard and network connector support WLAN. Then all you have to do is send a specific command, known as the 'magic packet' to a specified computer, and it will start up....allowing you to leave your renderfarm in a very low power mode until needed, started when you want from your control computer, and any tweaks can be done through remote desktop or WinVNC.

This is my current renderfarm, currently in the closet you see behind and to the left. The power is wired, and I have the keystone jacks in place there for gigabit ethernet, and am currently wiring the house for same. If you plan on long term usage, a rack setup might be worth the extra investment, as its one of those things you can add to as you can afford to. The cases with the blue light on front are 3u rackmount cases from Case Depot, the actual rack is from starcase.com. That is an 8 port KVM switch, and a Netgear 24 port 10/100 switch (which will be exchanged for a gigabit switch in the future). The cases are a bit pricey (the 3u's at case depot start at around $160, but that also includes a 300 watt power supply, which is more than enough to run a renderbox), but they also make it easy to replace internal components and keep going with the same case. This is also the result of several years of one piece at a time, and by staying with industry standard components, you never have to worry about running into a Dell or HP 'Oh, we're sorry, you have to buy 'OUR' part at a 300% markup'