go to folder options then file types tab, go down to (NONE) URL:HyperText Transer Protocol. click advanced (make sure it says open in the actions window) click edit, put in the browser you want in the second box, tick use DDE
Do you have SP2 installed? I noticed recently that an update in SP2 prevents certain applications from launching hyperlinks. I am not sure about which applications are affected, but I noticed that a lot of my ebooks that I created with e-book creator (not Adobe) no longer launch hyperlinks after the update was installed. I reverted back and they all suddenly worked.