In typography land you're supposed to have a seperate font file for each: Base/Italic/Bold/Bold+Italic. Thus you should have four copies of each font you have installed. Check your system and you'll see "Arial" "ArialBold" etc... You don't always have four fonts, especially for a silly font you find online.

With OpenOffice prior to 2.02 if you wanted a Bold/Italic font that you didn't have an actual file for you were out of luck. OpenOffice 2.02 implemented fake Italic/Bold to simulate those missing fonts. It works just like MS Office has worked for a while now. It's not a perfect solution, but it's good enough for 99% of users. Woohoo!