The one thing i can say about the public sector is once your in, it is so much easier to find other jobs in the public sector as you have an understanding of how the "system" works. My wife currently works for NZTE and thats a good organisation to get into if you want to do some traveling.
UberGunner is completely right there.
I've been in the public sector for three years. I currently work in an international relations team in a large public sector agency, and have been there part-time for almost two years while at uni. I go full-time into a graduate role in November. I don't have an IR or political science background either (honours in film and media studies, and architecture), but I have had a previous job in the public service which basically meant that getting another job (this one) was much easier. Contrary to many preconceptions of the public sector, my job is full-on, although I love it, and I will get some travel in the future (yay).
My first public sector job was as a result of getting a State Services Internship (I was offered a job post-internship). Unfortunately due to the current economic climate, that programme has been cut. Otherwise that is definitely one of the best ways of getting a foot in the door.
Given the current economic climate, I would also consider roles across the public service (provided they interest you), as UberGunner says, once you get in, it's so much easier to find other jobs within the public sector. A lot of jobs are often only internally advertised as well.
Keep in mind that you will probably do a lot of crappy work to begin with (e.g. OIAs), but it does get better. Before accepting a role, I would also find out what the agency is like in terms of staff development as well. And like any other role, public or private, there are great agencies to work for, and crap agencies - it pays to ask around friends, networks etc. who have had experiences with said agency.
Good luck!