Populate checkBox value to a textField

Hello,

I'm creating a form in Acrobat Professional 7. I have the following fields:

A checkBox called CB_Year1 with a value of 2008
A checkBox called CB_Year2 with a value of 2007
A checkBox called CB_Year3 with a value of 2006
A checkBox called CB_Year4 with a value of 2005

A textField called Year1
A textField called Year2
A textField called Year3
A textField called Year4

As the years are checked off, it'll populate into the textFields. I've got that part down. However I hardcoded each year to a specific textField. So if a year is unchecked, there might a blank textField in the middle. For example if only 2008 and 2006 are checked off it will currently look like this.

12/31/2008, _________, 12/31/2006, __________

I would like to write a javascript function that would append the years checked off from left to right. So for example:

12/31/2008, 12/31/2006

How do I go about this and if you can provde any examples. Any help is greatly appreciated.

Thanks!