Problem with layout shifting down when typing...

I just made the change from FrontPage to Dreamweaver.

Having created my layout in Photoshop/ImageReady I opened the site in
Dreamweaver.

Whenever I type anything on the page and press enter (to move to the next
paragraph) most of the other images on the page shift down.

Pressing delete doesnt bring it back up in line (as it used to do in
Frontpage).

Is there any way of locking everything so it doesnt move or do I need to do
something else.

Thanks in advance!