SBS 2000 not connecting to ISP.

I have Small Business Server 2000 set up and running. Internal mail is working, sending external mail works, receiving external mail works when Im already connected but its not connecting to the ISP to check for mail automatically. It seems exchange is set up ok, so is this a windows 2000 RRAS problem? I set up the server by following the built in wizards and Ive had no other problems except this. Please help because this is driving me round the bend.
Cheers
RW