how to delete old folders?

there is a section in the "backup.bat" file i need your help with

for /F "tokens=2-4 delims=/- " %%A in ('date/T') do set var=
%%B.%%A.%%C
md %var%
cd C:\%var%\

those lines create a folder with today date, with a specific format
and then i use xcopy to backup the files to this folder

after X days of backuping, i have X folders on the hd, for example:
20.07.2006
21.07.2006
22.07.2006
and so on....

i need to add a section that check the hd disk space
if it's less then 1 gb
then it should delete the oldest folder

i will appreciate any help, 
thanks very very much 
Assaf M.