I would KILL to have a housekeeper... just can't afford it though *sigh* I would say bi-week though as far as things like windows/floors and weekly on the Kitchen/Bathroom things (those are my worst two rooms in the house, I can't seem to keep them clean for longer than 2 minutes!!!)
I have one of those Swiffer vacuum thingys and it's awesome for quick touch-up's on the floors & carpets to help maintain until "cleaning day" Both of my kids LOVE to help mommy with the Swiffer, they think it's so very cool!