Start with this:

http://www.ebay.com/sch/PC-Desktops-/179/i.html?_nkw=eeebox+...

Add in this:

http://www.insanelymac.com/forum/index.php?showtopic=199658

And get this:

http://www.youtube.com/watch?v=2li6mOtGBFY

The tricky part for me was that due to to Asus' partition of the existing Seagate drive (it's got a hidden bootstrap so that you can positively destroy the eeebox and have it come back to life) I didn't get any joy until I replaced the HD (which I had sitting around - went SSD on my mac pro and then upped the size, so the old SSD went into my Mac Mini and the old Mac Mini drive had been sitting around). From there, things went swimmingly. At least, 10.6.3, which I happened to have a retail distro of lying around. Haven't been able to turn up the kernel patch for 10.6.5 (or 10.6.8 for that matter).

I did replace the wifi card with one that Apple uses and calls "airport." That is a bit trickier:

http://vimeo.com/1690401

Another handy thing is a friend of mine upped his Macbook Pro from 4GB of RAM to 8GB, giving me two 2GB DIMMs. That 4GB went into my Macbook, freeing up two 1GB DIMMS. Those went right into the eeeBox.

So far, I'm out-of-pocket $107 and shipping on the eeeBox and $20 on the wifi card. The thing is really only running Earthdesk and Lightsoft Weather Center, though, and it's a long way from taxed.