If I understand your question, you want what I call a dependant field  on
you list. This is on my list  of "Platform Busters" because SharePoint
2003 doesn't support dependant fields  out of the box. It can become
quite tedious to make them for yourself using JavaScript.

Any suggestions regarding alternate technologies I could look at then?

Have you looked at using InfoPath and then use an event handler to populate your list. We did this with a Conference Room/Classroom Scheduling process. The InfoPath form has dependant fields  that open other fields for input;e.g., if the Video Teleconferencing box is checked, additional input fields open for information that is required for the VTC. The event handler post the information to an Event list  in a pending mode.

InfoPath and ASP.NET are your best alternatives. Or you _can_ create  a
new list  template definition (lots of CAML in there).