</form> tags are block level elements in HTML, which, be default, have line breaks around them.
With CSS, you can set block level elements to be displayed as inline, which should eliminate the line breaks.
form {
display: inline;
}
As an alternative, you can omit the ending </form> tag if you dont have any other forms below it, AND if you open your form like this:
<form method="post" action="/action.php" />
Note the closing /> which indicates an empty element...