Outlook Web Access

I have recently installed OWA. Internally it works fine, externally its not so good. trying to access via the ip e.g. http://192.168.1.1/exchange/ gives me a page cannot be displayed error. I have the lastest service pack, exchange 5.5, and IIS 4running.

How can I enable it to be viewed externally? Please help me someone!!

Steve
smcculloch@citacom.co.uk