[mɑːrk ˈodəgɑrd]

I have replicated Piotr's problem on a different PC using earlier versions of both W95 and Netscape (4.5 in this case). I got squares. However, on this machine with a later version of W95 and using Netscape 4.7, the script a, [ɑ], ː and the schwa display perfectly. It displays flawlessly in MS Outlook Express as well (I'm composing this in OL).
One I have noticed is that the combining diacritics tend to not center themselves correctly over or under the letter. This might also be an artifact of what browser you use, and what edition it is.