I just bought an M5N and installed WOW. 768mb RAM, XP Pro, swap file turned off, all nonessential services disabled, 1.7ghz cpu.
The game can be run in this setup with all the detail settings turned all the way down, and played at 800x600. I probably average about 20fps with this setup. Slightly more when just running around, slightly less when fighting. I just started playing so I haven't gotten to any complex battle scenes yet; I suspect it won't do so well there. The game is certainly playable though, at least so far.