You will be hard pressed to create something as good as VBulletin! You can however, create something very very simple yourself, one of my sites F1 Community is still in beta and has a forum written in PHP and my SQL.
If your looking for something basic to build from, or even just use, openBB is pretty good. Although its only in beta1b, I use it and there don't seem to be any critical bugs. Might be worth a look? http://www.openbb.net/