If you need more precise instructions:
Highlight the data with 2005 sales - click Insert - Chart. Select Line Chart type - select Chart subtype: you need 'Line with markers displayed at each data value'.
Then next - Series tab - Enter Name field (for ex: 2005 Sales). Select Category X values, then click Add (series) - choose Series2 Name (for ex: 2004 Sales). Choose Values for this series by clicking on the small square to the right of the field, highlighting data with 2004 sales and clicking on the square again. Click Next.
Then you may play a little with various chart options, choose chart location and click finish.
That is all.