Real HTML

I bet this question gets asked alot but i guess im not using the right search terms.

I’m writing a post on my blog in HTML mode.. but it ignores my breaks lines and randomly adds in paragraph tags even though i didnt put them in. so now when i try and validate there are all these paragraph tags that arent opened or closed right and im not coding for any?

how do i disable wordpress from inserting its own html into my posts… i had an old 2.0 blog and I thought there was a tab or check box somewhere that used to let me do true html.

any help would be great, im having a big coding error and i cant sort it out until the page starts behaving like I coded it and i can get rid of all these paragraph errors..