Have you considered the EFiX dongle? A friend of a friend built a machine with one and, from what I hear, it actually works. This is despite the guy's poor PC-building skills. He apparently needed to watch youtube videos of how to install a Socket 775 processor during the build.

I'm intrigued by the device, but I think I would still rather spend the money on a real Macintosh. Even if it was a Mini. Personally, I find the Mini more appealing than an iMac because they now have dual monitor outputs and appear much easier to upgrade.

On a related note, I just got done upgrading a cast-away Sawtooth G4 for the sole purpose of video editing. My video work is done in iMovie and iDVD, but it works perfectly fine for those programs. The only time it's really bogged-down is when compiling a DVD. I basically have to set everything up, start the process, then go to bed, go to work, and it might be done when I get home. I got the machine for ~$50, 1GHz G4 upgrade was $170, 2GB of RAM $50, and a hacked PC nVidia 6200 AGP card for $60 or so. Not too shabby, really. A G4 Mac Mini would have cost roughly the same, but I can actually put cards and desktop hard drives in this one...