Easiest way to do this.

Place your cursor in the cell you want as your starting number.
Type your starting number.
Make sure you are still in the same cell.
From the Edit menu, select  Fill, and then select Series
The Fill Series dialog box will open.
Set the Series in to Column
Set the Type to Linear
Set the Stop Value to 1000
Set the Step Value to 1. (5 if you want to count by 5: 5, 10, 15, etc)
Click OK