Make field read only untill value within pciklist is choosen

Question

Hello,
I am trying to establish if it is possible to make a field read-only until a value within a pick list is chosen. Basically we have a pick list called structure and if the field value called "Aligned" is selected then I want the text field called Aligned Name to be available for import all other times this field should not be available.
Has anyone done anything similar? I'm guessing that this could only be achieved through WF but I haven't been able to find any code to make fields read only.

Answer 1

For those of you unable to download the document from MetaLink3 here it is:
As an example to illustrate this requirement, let’s say that once there is a checkbox field called "My_Check_Box". When this field is checked, the "Account Type" field need to become a required for entry by the user. To do this follow these steps:
1. In the Admin> Application Customization, select the appropriate Object and go into the Object Field Setup.
2. Edit the field called "My_Check_Box" and enter a Field Validation expression so it uses the following expression:
=[<bMy_Check_Box_ITAG>] AND NOT([<AccountType>] IS NULL AND [<bMy_Check_Box_ITAG >]='Y')
3. Enter an explicit error message.
This expression means that when the checkbox field is checked, the Account Type becomes required. Your custom error message will be raised when checking the checkbox, leaving the account type unpopulated and trying to save the account record.
4. Edit the Account Type field and enter the following expression as Field Validation:
=[<AccountType>] AND NOT([<AccountType>] IS NULL AND [<bMy_Check_Box_ITAG >]='Y')
5. Enter an explicit error message.
That validation handles the user case where a user changes the Account Type value from a NOT NULL value to a NULL value. Your custom error message will be raised when emptying out the account type from a populated value to nothing while the checkbox is checked and trying to save the account record.
Note that the expression in both fields validations begins with the field variable on which the statement is being written.**