Teaching abroad can add weight to your CV but it depends on how you sell yourself. The key questions are: why did you do it, and what do you think you will gain from the experience?
As to finding a job on your return, that depends. Consider the job market and how easy you would find it to change schools if you were still working here. Work out whether the school year where you might teach abroad follows that of the UK or to a different cycle. Would you be prepared to fly home for an interview? The job market in parts of the UK may be difficult for the next few years and will be more open as schools compete to replace the teachers who will be retiring in big numbers, probably from 2007 onwards.