Formatting Figures in LaTeX

What I want is to give my graph a label of 'Figure 1.1'

 \begin{figure}
 \caption{}
 \includegraphics[width=5in,scale=0.5]{picture1.pdf}
 \end{figure}

However I this produces 2 problems:

1) Before I just put

   \includegraphics[width=5in,scale=0.5]{picture1.pdf}

and that inserted the picture nicely into the middle of my page of text. But using the above procedure seems to force the picture to the top of my page. Is there someway I can disable this?

2) The labelling of the figure comes out as 'Figure 1.1:'. But I don't want the colon to be there. I simply want 'Figure 1.1'. Is there someway to supress the colon?