date & time calculation

I have a datetime-field: date1 (dd-MM-yyyy)
and I have a text-field: time1 (length = 4)

How can I achive the following field: calculation: dd-MM-YYYY HH:mm

so I fill in: date1: 12-12-2003
and I fill in: time1: 1128

than I want result: calculationfield: 12-12-2003 11:28

Can this be done?

found it! :D

var a = date1
a.setHours(utils.stringMiddle(time1,1,2));
a.setMinutes(utils.stringMiddle(time1,3,2));
return a;

Thanks anyway!