If you can store your values in a table, you can do this easily as long as you get each detail correct.
Set up your AccountNumb table with at least two fields: AccountCode and AccNumb.
Create a relationship linking your Account code field in your main table to AccountNumb::AccountCode.
Define a value list that specifies AccountNumb::AccNumb as the source of values.
Click the "include only related values starting from" option and select the name of your main table from the drop down.
Load your new table with values.
Format your Account Number field to use this value list.
Now when you enter '2' as the account code, should should see just those values in the AccountNumb table that have "2" in the AccountCode field of that table.
Works great!!! Thanks for the reminder about tables.....