Blocks incorrect location on Mac

I just began some work on an existing drupal 5.x site, which is running a custom theme. Because I just began, I do not have access to the actual theme files yet, though I will soon.

At the moment, blocks on the right side do not display correctly on my Mac, with both Firefox and Safari. When tested with Firefox on Windows or Linux, the blocks are correct. Another issue is the last menu item (menu is across the top, to it's the menu item farthest to the right) is not displayed at all, even though it is there when I view the page source. When I resize the browser window, the resize is correct.

My question, where should I start investigating this type of problem? Would there be log entries, php or css related? Or maybe a combination of specific modules that can cause block display issues?

Any pointers on where to start is appreciated.

Cheers,