Month, Day and Year source code to lag behind approximately 30 days

Hello,

I have been using a hacked form of the source code below for a while to display "incrementally" the month, day and year that is one month old. This has worked OK up until new years eve, when I broke it.

I have the day and month sorted. But I can't find a solution to keep the year lagging exactly by one month during change over to the new year.

For example - to explain myself a little clearer: Today's computer date on my PC is "January 1, 2010" and I would like the source code to calculate and display on my web server page the "December 1, 2009", then on the actual future date of "February 1, 2010" change the year over from 2009 to 2010.

What I'm tying to do is simply have javascript calculate (from the users computer on the fly) a date that is approximately always one month old/previous. So the actual date displayed on my web page is always one month behind the actual current users computer day, month, year.

Web server Display format:
[December 1, 2009]

var months=new Array(13);
months[0]="December";
months[1]="January";
months[2]="February";
months[3]="March";
months[4]="April";
months[5]="May";
months[6]="June";
months[7]="July";
months[8]="August";
months[9]="September";
months[10]="October";
months[11]="November";
months[12]="December";
var time=new Date();
var lmonth=months[time.getMonth() + 0];
var date=time.getDate();
var year=time.getYear();
if (year < 2000)
year = year + 1900;
document.write(lmonth + " ");
document.write(date + ", " + year);

Code (markup):

Thanks for reading and your help,
Cheers
JC