Brazil is a huge country and the pronunciation can vary slightly from region to region, but in general you will not have problems understanding regional accents.
Don't worry too much about regional accents as you most probably will have your own foreign accent. It is important that you pronounce words correctly so you will be able to communicate with the local people and be understood.
If you like any regional accent, you will pick it up easily if you live in Brazil for a while.
My CD-ROM Course includes a complete and very detailed pronunciation guide, which can help you improve your pronunciation. Check it out!