Suppose you are looking at a worksheet which contains dates which can't be formatted as "real" dates because of their structure:
Select the date(s), and use Data tab, Text-to-Columns, [Excel2003:Data|Text to Columns]
Which brings up the Text-to-Columns wizard:
Even though the dates are fixed width, in this case you can simply click "Next" twice.
In step 3 of wizard Select Date, YMD:
If you click Finish now, the result will replace the dates. You can select another destination cell:
Here's the result:
