Make sure you brag to him about your sexual exploits. Give plenty of details.
But seriously... It really depends on your friend'* general disposition. I never really cared when classmates dated my sister because I wasn't all that protective. However, he might have a father-like relationship with her, in which case you need to tread lightly. Ultimately, if you treat her with the respect that any woman (or human being) deserves, you shouldn't have any problems. Be a kind, caring boyfriend, and your buddy might end up being your brother-in-law somewhere down the road.
1997 SE w/SLE package
"White curse? I think it'* more like.... WHITE FURY!" - MyLittleBlackBird