The first thing I'd do would be to preflight the thing and look at fonts in the resulting window. Sometimes you get TTF and T1 combined in the same document. That's especially true if someone copies in something from Word or such. Just last week I got something from the graphics dep't at one of the real big banks with the T1 TTF combo, along with a 100 dpi jpeg picture for a 203 dpi newspaper ad - wonderful. Picked up the font combo on a preflight.
Of course, I'm assuming that the designers used all cmyk and no rgb, another common problem when pasting in from a word precessor.
The drop cap shouln't matter because the offending lines should be well below it or in a different column.
If you're printing postscipt first, you might check the Graphics and under Fonts make sure that Complete is selected nest to Download and possibly check PPD. You can also distill the resulting postscript and have Acrobat check for offending postscript. You might also check for any updates to the RIP from the maker.
I'm guessing that it's something that you're getting included with what's sent to you as opposed to all the time. If two or even five things get botched and the others don't, It's usually not you but the person who sent it to you. So you might want to check the offending things against stuff that's running true. Things like paragraph styles, etc could be goffed up - something that's real hard to check.
Using OSX 10.3.9 on a G4