Conditional Formatting Option:
1) Select cell B2
2) Go to Format | Copnditional Formatting
3) Select 'formula is' from the first drop down list
4) enter the formula:
=weekday(b2)<>2
5) click the format button, select the patterns tab & a colour of your choice.
6) Click 'OK' twice...
This will highlight B2 if the date entered is not a Monday
Data Validation Option:
1) Select cell B2
2) go to Data | Calidation
3) Select 'Custom' from the 'Allow' list.
4)In the formula box, enter the following:
=weekday(b2)=2
5) Set up the input messages / error alerts you want.
6) Click OK
This will throw up an error message if the date entered is not a Monday.
Paddy