Here is an example config I use. Look at the last line with "firstDay: 1".
I think using sytax like this to specify datepicker options looks better ;)
$('#datepickerfield').datepicker({
constrainInput: true, // prevent letters in the input field
minDate: new Date(), // prevent selection of date older than today
showOn: 'button', // Show a button next to the text-field
autoSize: true, // automatically resize the input field
altFormat: 'yy-mm-dd', // Date Format used
beforeShowDay: $.datepicker.noWeekends, // Disable selection of weekends
firstDay: 1 // Start with Monday
})