1) Never, ever, ever resize images like that (using CSS or HTML). Always, and I mean always, resize your images locally and them upload them to the server. So you’ll probably have multiples of each image, image_one_thumb.jpg & image_one.jpg. Doing it as you’ve done will cause images to look warp and stretched. Gross.
2) You have line breaks between each image, that will certainly cause some problems. In Firefox, for example, it’s causing the "Step Down" problem.
3) You don’t need to have those images wrapped in a <p> tag. You’ve already got them wrapped in a div, the <p> tag will only cause editing problems later on. Especially if you’re using that <p> tag for positioning the images.
2 and 3 are defaults caused by WordPress I’ll see if I can edit that, and your 1 issue is for a client, he doesn’t want to resize his images every time he makes a post so I would appreciate it if you didn’t get on my case about it. I don’t know any other way to do it, so maybe I’ll look for a solution