In Excel for Windows, a date is a serial number, where 1=Jan 1, 1900.

2=Jan 2, 1900; 29=Jan 29, 1900; 8/10/2011=40765, etc.

This is the reason you can do math with dates and the answer will be in number of days. Try it... put your next birthday in a A1. Put today's date in A2. Create a formula =A1-A2. the answer is how many days til your next birthday. (If the answer looks like a date, just change the format to number.)

No matter how you type a date in a cell, no matter how you format it, the formula bar will show it as 1/5/2008. If it doesn't, then Excel doesn't recognize that it is a date, and that is a big big problem.

Type in the date however you find easiest to type and then format it the way you like to see it.

By the way, times are just fractions of dates... Today's date is 40,765. Today at noon will be 40,765.5

Sorry Kimberly, all you said is absolutely true, except this: " Create a formula =A1-A2. the answer is how many days til your next birthday."
The problem is that A1-A2 is a negative number, and the result is the age in days , and not how many days til your next birthday.

As for kjxavier problem, my guess is that the cell in which you have directly entered date as 01/05/2008 is formatted as text, and not as date, this is the reason excel says the dates are different.
You can solve the problem using in your comparrison formula to convert text to date:
=DATE(RIGHT(L16;4);MID(L16;4;2); LEFT(L16;2)) (-just replace L16 with referrence to other sheet) , and now, when you compare the date in this sheet with the result of the formula, will say they are the same...
Hope this solves your problem...