I would pass on it if you plan on trying to use VLC - IIRC the og's only support 480p content reliably. I might hold out until you can find a cheap 2006-2007 Intel Mini.
/edit:
For 1280x720 (720p) video at 24-30 frames per second:
QuickTime 7 for Mac OS X:
1.8 GHz PowerMac G5 or faster Macintosh computer; 1.83 GHz Intel Core Duo or faster
At least 256MB of RAM
64 MB or greater video card