Js Function To Find The Difference Between Two Dates?

i've written a js function to find the difference between two dates. the format being used is dd/mm/yyyy hh:mm. The function returns correct value when give one set of values, but go wrong with another set. examples are given below.

set 1 : Time 1 = 24/02/2011 09:30 , time 2 = 24/02/2011 16:00

Output is corret here. It gives 6 Hours & 30 Minutes (after converting the difference)

set 2: Time 1 = 24/02/2011 09:30 , time 2 = 25/02/2011 16:00

Here, it gives 31 days, 6 Hours & 30 Minutes. My code is given below. Also the alert of dates display strange values. Don't know if it is timezone issue.

function compareDateTime(frmtime,totime)
{
var date1 = new Date(frmtime);
var date2 = new Date(totime);[code]......