You shouldn't really need a vpm to create a audible account just use the audible 30 day trial link,create a new account, use addresses from those fakename generators out there, and try your own creditcard. Itunes actually checks which country you have chosen and where the creditcard is from so there the country matters but I do not believe audible does it yet. At least audible makes a surcharge to see weather your card is fake or not before it lets you download books even for free trial, so as you already are downloading the book, it looks like your card does work.

For all the audible books that people own I suggest they use inaudible to convert them to whatever formats they like. .m4b, mp3 or what you will, no more hassle with buggering about with the right player, authentication and such.
grryf