Assuming that you have stored the dates in a format that Excel recognizes as a date, all you have to do is compare them, e.g., IF(A1<>A2,"Dates don't match","Dates Match")
Excel stores dates and times in the same variable with the date as the integer (whole number) part and time as the decimal part.
If your cells with dates are formatted as dates without a time format it is possible that the cells contain time information as well,but it is not visible and as a result, two apparently equal dates will not be equal due to different times.
26 January 2010 is stored as 40204 and 12 noon is stored as 40204.5 i.e., half way through the day.
To ensure correct matching of dates, either ensure that dates are 'pure' or use the INT() function to compare only the integer part of the value in the cells:
IF(INT(A1)<>INT(A2),"Dates don't match","Dates Match").
To test if a cell containing a date has been recognized by Excel as a date and is not just a text representation of the date, see if the cell changes in response to different date formats, or try formatting it as a number. Recent dates will have a number around 40000.
The default date system in Excel starts with 1 for 01-January-1900