That is a very good question. I think times are changing a bit now, a few years ago there wasn’t really an academic path into this job (except through, perhaps library science for IA). Now there are good postgraduate courses out there in IxD, IA etc. That might be one option worth considering.

Otherwise, there are plenty of real world opportunities to get into this field. One advantage is that because there are so few courses on IxD, IA etc, few people come into the game professionally trained. A good friend of mine trained as a visual designer at my previous company and did a bit of IxD. She now is a Senior IA. So going in as a web designer/visual designer and making it clear to your new employee your career aspirations is definitely a good path.

Otherwise, remember there is a deep shortage of people in the field. Keep an eye out for junior positions, and apply for them. To help improve your chances I would consider reading some classic texts such as ‘About Face 3′ by Cooper et Al. Then, off your own back, use the knowledge you have picked up and have a go at a UxD excercise (such as a Heuristic Evaluation of a famous website, followed by a proposed re-design of that website based on the results of your HE). This sort of thing can be added to your portfolio and I promise will deeply impress a prospective new employer looking for a junior IA/IxD/UxD position. It will show initiative and skill.

Hope this helps!

Thanks for taking the time to comment much appreciated! This particular heuristic comes from a paper by Deborah Mayhew in 1992 called ‘Principles and guidelines in software user interface design’.
Hope this helps, if you have any further questions please don’t hesitate to ask!