Mathew,
Also consider the CommandSoft’s Fibrejet. I have almost EXACLTY the setup you are looking to build – three G5s, a gigabit network with a file server, an Xserve Raid, a SanBox fibre switch, and FibreJet instead of Xsan. It would suit your needs perfectly, be much more simple to set up and is faster at most things than Xsan is (though I have not tested Xsan directly, I have tested other SAN software that works the same way. Especially on large projects, Fibbrejet is WAY faster). Cost is about the same. CommandSofts support is great and you can always get someone on the phone or a fast reply to an email. I put all this together myself. CommandSoft will also do some turnkey stuff I think, and they will certainly help you with configuration. Its really not all that difficult.
Feel free to contact me directly if you have any questions.
Chris(at)outpostpictures.com
Chris Tomberlin
Editor/Compositor/Owner
OutPost Pictures