Include the necessary files by adding this to your model or controller:

response.files.append("http://ajax.googleapis.com/ajax/libs/jqueryui/1.7.2/jquery-ui.js")
response.files.append("http://ajax.googleapis.com/ajax/libs/jqueryui/1.7.2/themes/ui-darkness/jquery-ui.css")

Copy the widget code to your model:

def date_widget(f,v):
    wrapper = DIV()
    inp = SQLFORM.widgets.string.widget(f,v,_class="jqdate")
    jqscr = SCRIPT("jQuery(document).ready(function(){jQuery('#%s').datepicker({dateFormat:'yy-mm-dd'});});" % inp['_id'],_type="text/javascript")
    wrapper.components.extend([inp,jqscr])
    return wrapper

Apply the widget to a field:

db.define_table("test",Field("posted","date",widget=date_widget))

Try it out in your controller:

def index():
    form = SQLFORM(db.test)    
    if form.accepts(request.vars,session):
        response.flash = "Got it"
    all = db().select(db.test.ALL)
    return dict(form=form,all=all)

Demo application (right click/Save As): Download