Just to add on place's comment...
usually things that appear on ff are identical on opera and safari.
You don't have to worry about images, borders or any other elements of your theme.
Problems start happening with position and placement.

this is where IE dies.
It doesn't understand positioning settings ... apart from absolute settings.
but to set up your site all absolute you need a load of patience , and you need to have everything identically placed.

One thing that is also a problem (but obviously microsoft think its an improvement) IE has this ... text rendering system thing... It makes your letters smoother and "easier" to read ... but this rendering makes the letters a tiny bit thicker... in the end it adds up to a big gap,... usually you gotta fix it with paddings.


All in all its not easy being a designer.
i wonder how the browsers will react to CSS3

Thanks for the help friends
I'll use this tricks in my designs and try them myself
Thank you.