We use Exchange Server 5.5 public folders heavily, but we have no way to change public folder permissions from within Microsoft Outlook Web Access (OWA). Do later OWA versions support this functionality?

No, neither Exchange Server 2003 nor Exchange 2000 Server provide a way to change public folder permissions directly from OWA. To change the folder permissions, you must use either Outlook or Exchange System Manager (ESM). The PFAdmin command-line tool, which lets you set public folder permissions from the command line, might also be useful because you can drive it from a custom Web page. At worst, creating a public folder in which users request permission changes that an administrator must then handle might still be an improvement over the current situation.