ERROR check if a date set entered violates a previously entered date set

[buzz]

I am developing an Excel spread sheet that has date sets, not
necessarily entered in sequential order. I want an ERROR CHECK if a
date set entered violates a previously entered date set.
What I was looking for is a set of dates could not be typed in as
follows:
1/10/04 to 4/20/04
2/10/04 to 3/20/04
The second date falls within the fist and should be invalid, setting
off an alarm or not allowing it to be entered. I was thinking about
making the date entry idiot proof so that one could not enter date
sets within or covering dates sets previously entered. This one really
throws me, please help.

 

[Mark]

Are the dates in separate celss or is the from to date in
one cell?
If the latter then it is text. If the former then you can
check the date against other entries.

Even set up the worksheet with an entry macro that chwecks
the data.

Mark