A few words of thanks would be greatly appreciated.

Excel - Display multiple columns in a validation list

Excel 2003 and earlier version
Excel 2007 and above

We'll need to trick Excel to accept to create a validation list with multiple columns

Example to show the range A1 to C20 (20 rows and 3 columns).:
Start by naming the range A1 to A20 as "List"

Highlight A1 to A20

Excel 2003 and earlier version

Insert / Name / Define
in the Name text box in the workbook: name the range as list
create a list of validations in E3 (Data / Validation, in Allow: select "List" in Source: type =List)
Open the Name manager Insert/Name/Define, select the name of the range (List)
In "Refers to": Change the values from $A$1:$A$20 to $A$1:$C$20

Excel 2007 and above

Data tab / Data Validation module
in the Name textbox : name the range as List
Create a list of validations in E3 (Data/Validation, in Allow: select "List" in Source: type =List)
Open the Name manager: Formula tab/set name/Name Manager, select the name of the range (List)
In "Refers to": Change the values from $A$1:$A$20 to $A$1:$C$20