Dialects are variants of a language. They have different vocabulary, sounds, and sometimes grammar, when compared to the "standard" form of the language.

Registers have to do with the level of correctness, politeness or intimacy one uses. That is usually totally independant of dialect.

For instance, if speaking to someone with whom one has a dialect in common (IE: both from the deep south), one will probably speak to them using this dialect, regardless of who this person actually is. One will, however, alter one's register to reflect the status of the other person. If it is a close friend, one's speech will be more casual and relatively intimate. If it is a professor, one will be more formal and may use honorifics.

Register has little to do with the speaker's culture, regional or ethnic identity, or sense of local pride. It is more a matter of showing the appropriate degree of respect (or lack thereof) to someone else while speaking.