session problem

bapi

Hi, everybody I am running a website based on local information and user communication. Here local user asa well as other user resigter and they have their account which gve them access to diffrent tools. And now I decided to use the best and lighted weighted forum. But i don't want my user to signin twice, one for their account and once for forum. So what should i change to that my user don't have to login twice. Please help