Using a list box in a query

I want to make the parameter for a query a list box containing the contents of a table. The table is a list box withing a second table outling costs. The users of the second, bigger table are not acclamated with access or query behavoir so I thought it better to let them select which department they want as opposed to typing in. Below is the code so far:
SELECT [Cost Analysis 2004].*
FROM [Cost Analysis 2004] INNER JOIN Departments ON [Cost Analysis 2004].[DeptNumber]=[Departments].[DeptNumber]
WHERE ((([Cost Analysis 2004].[DeptNumber])=[What Department?]));

How can I make the querey parameter a pull-down menu?