You would do something like:
Dim pPolygon as IPolygon
pPolygon = new polygon
Dim pPointcoll as IPointCollection
pPointcoll =pPolygon
Creat your points:
dim pPoint as IPoint
pPoint = new Point
pPoint.x = 1
pPoint.Y=1
Then you add your points to build the polygon:
pPointcoll.Add(pPoint)
Duncan