Form elements do vary considerably between browsers and there’s little you can do for the intrinsic differences that may crop up as not all parts of the controls can be accessed via css and what you can access depends on browser also.
However you should be able to get quite close and I don’t see any difference in the size of these inputs in Safari/Firefox and IE.
You may need to provide a specific example so we can address the issue more directly:)
Things like the alignment of buttons due to Safari’s rather different button style. Is I position a button say 100 from the left it is further over in Safari than it is in the other browsers mention.
We’d need to know what kinds of problems you are seeing in Safari in order to help.
To be honest Safari works pretty much out of the box anyway so it sounds like you are doing something wrong if you are getting a lot of problems or you are just unlucky