from the Excel help file, is this what you need?
Restrict cell entries to the data from a list
1 On the same worksheet, type the list of valid entries down a single column or across a single row. Do not include blank cells in the list.
2 Select the cells that you want to restrict.
3 On the Data menu, click Validation, and then click the Settings tab.
4 In the Allow box, click List.
5 In the Source box, enter a reference to your list of valid data.
If you want to select from a list of the entries when you click a restricted cell, make sure the In-cell dropdown check box is selected.
To specify that the entry is not valid if the restricted cells or the cells that contain your list of valid data are blank, clear the Ignore blank check box.
6 To display messages to prompt for entries and to explain or prevent incorrect entries, specify the types of messages you want on the Input Message and Error Alert tabs.
To omit display of messages, clear the Show input message when cell is selected check box on the Input Message tab, and clear the Show error alert after invalid data is entered check box on the Error Alert tab.
· If the list of valid entries is short, you can type them in the Source box instead of typing the entries on a worksheet, separated by the Windows list separator character (commas by default). For example, you could type Low, Average, High in the Source box instead of entering the three words on a worksheet.
· If the list of valid entries might change, name the list range, and then enter the name in the Source box. When the named range grows or shrinks because of changes you make to the list on the worksheet, the list of valid entries for the cell automatically reflects the changes.
· If the list of valid entries is in another worksheet or workbook, define a name for the external data on the active worksheet. In the Source box, you can then refer to the name on the same worksheet. For example, if the data you want to use in a formula is in cells A6:A12 on the first worksheet in a workbook named Budget.xls, you could define the name ValidData on the active worksheet to be =[Budget.xls]Sheet1!$A$6:$A$12 and then enter =ValidData in the Source box. For information about defining names, click .