‘br’ vs ‘p’ in post editor

Sorry if someone already covered it, but I did a few searches and hopefully am still not missing something HUGE. My apologies, if I have, I am very new to WordPress (2 weeks).

I am having problems with the WP 2.0 post editor. Sometimes when I hit enter I get a ‘p’ and sometimes I get a <br>. It is messing up my fomratting and then I have to go through the HTML editor and redo the HTML.

Has anyone else run into this?

Thanks in advance,
Robert