So if your text is in the format dd/mm/yyyy you'd convert it to a date using:
var this_text = '13/07/2010';
var this_date = new Date(this_text.substr(5,4),this_text.substr(3,2)-1,this_text.substr(0,2));
Alternatively you could use a regular expression to slit the date into an array containing the day, month and year separately. and then load them into the date from that.
Once you finish playing with the date and want to convert it back to text you'd use:
this_date.getDate() + '/' + (this_date.getMonth()+1) + '/' + this_date.getFullYear();