I have the 8900 and have an 02 e-mail account set up as POP3, and have my work Exchange address sent to it, when i get e-mails now it seems to appear twice on my Bberry. Once in the E-mail icon and again in the messages icon. Why is this happaning plz.

Because the 'Messages' icon is a catch-all inbox and will gather messages from every messaging service available to your device. (BES, BIS, PIN, SMS, etc.)
That's the way it's designed to function.