It seems alot of people are facing problems with the public folders in Exchange 2007.
As per Microsoft documentation earlier they are removing public folders from Exchange 2007.
Actually it only exists if you had Exchange 2003/2000 in your enviornment.
In your case Exchange 2007 give you control over the public folders only using the Power Shell, but has no GUI for that.
It seems to be a sad change that Microsoft has implemented as many companies are highly using Public Folders, though the good news Microsoft will bring the full power to public folders to their Exchange 2007 in SP1 for Exchange.
SP1 release estimated date is in Feb. SP1 beta 3 has just been released few days ago. For now, your only way to manage them is using power shell as you have removed Exchange 2003 from your setup, else Exchange 2003 would be the best place to manage it.
I hope that help.