Hi Chris,
You can consider either User Forms (se relevant TestComplete help topic) or some configuration file processed before test start.
Also (some?) scripting languages support simple input forms like InputBox() function in VBScript or BuiltIn.InputBox() function provided by TC.
From the conceptual point of view, configuration file (or custom parameters of TestComplete command line) seems to me the best option as it makes it possible to execute tests unattended, but you might consider UserForms better fit your requirements.
