There is no safe way all you can do shut down the feed from the mains. You will have no water coming from the taps but water will be in the pipework but not under pressure.
Drain ALL tanks and central heating system.
If you then get a freeze up the damage would be neglagabl to an unchecked mains feed flow.
You now have to hope that the pipes under the floor are lagged.
Rob
Rob, November 2005
edit
I can answer this question...
Winterizing Home...shut water off..drain pipes safely?