This example sets the print area to cells A1:C5 on Sheet1.
Worksheets("Sheet1").PageSetup.PrintArea = "$A$1:$C$5"
This example sets the print area to the current region on Sheet1. Note that you use the Address property to return an A1-style address.
Worksheets("Sheet1").Activate
ActiveSheet.PageSetup.PrintArea = _
ActiveCell.CurrentRegion.Address