I already posted much of this in another thread, but I figure that someone else might find this here and find it useful:
I have had success booting FreeNAS 8.0.3 on my ex490!1. I downloaded the FreeNAS installer ISO.
2. Then, using my Mac and Parallels, I booted off the ISO and had it install to a small USB stick.
3. I then took that USB stick and plugged it into a relatively recent windows laptop and booted off the USB.
4. I turned on the network interface using the CLI and saved the settings.
5. I moved the stick to the bottom rear USB port on the ex490.
6. If I left all four HD's in their trays, the ex490 booted WHS, which isn't, of course, what I want it to do.
7. I powered off, ejected the system drive, and then powered on again.
8. FreeNAS booted this time and I was able to access the web GUI from a remote machine!
Now to set this thing up properly so I have a working NAS again.... It definitely doesn't seem as easy as the initial WHS setup was, but I already have the hardware and it's cheaper than buying an empty NAS enclosure. If I can get this working, I think I'll buy a blank drive and pull the WHS system drive permanently (or at least until I give up entirely on the hardware and want to sell it).
My problem before was that I had assumed that the FreeNAS ISO was a working system and not an installer.
Can someone correct me if I'm wrong about this, but the ex490 only has one RAM slot, right? Therefore the maximum amount of RAM is 4 GB (i.e. no ZFS possible)?
Also, slootj, were you able to get Time Machine running? If you're on Lion, you'll probably need to upgrade FreeNAS as it has more stringent requirements for what volumes it will allow to be used:
http://support.freenas.org/ticket/535