Recently in the Apple forums a user complained that he couldn't do Romanian in MS Word 2004 using the standard fonts Arial and Times New Roman. At first I was puzzled, since MS specifically provides special enlarged versions of these fonts with Word that contain Arabic, Hebrew, Greek, Russian, and Vietnamese in addition to more common Latin languages. But sure enough, when I looked more closely, I found that Version 3.05 of Arial and Times New Roman are missing the letters s-comma and t-comma required by Romanian.
It turns out that updated versions of these fonts with the Romanian characters added are available to WinXP users via download from MS since Dec. 2006, and that the new versions are also automatically included in WinVista. Unless you can get copies of these, you'll have to use other fonts for Romanian in OS X -- Courier, Geneva, Helvetica, Hoefler, Lucida Grande, Monaco, Palatino, and Times should all work, along with various downloadable fonts that cover the whole Latin range, like Doulos, Gentium, Charis, and Everson Mono.
See this article for another issue relating to Romanian in OS X.