Yes, you can have the x values as dates.

1) List your dates in a column.
2) List your y values in the column to the right of your dates
3) Highlight the Dates and y values and click on the Chart wizard icon.
4) On step 3 of 4 of the chart wizard, click on the Axes tab.
5) For the Category (X) axis, select Time-Scale.

This will make Excel treat the dates as vales and not categories.

You can read more about this here:
http://peltiertech.com/Excel/ChartsH...ValueAxis.html