You can upgrade to Office 2004, which will install a Mac-friendly
version of PMingLiU.ttf. See here:
http://www.yale.edu/chinesemac/pages/applications.html#Office_2004
Note that Office 2008 is due to be released in January, though I'm not
sure what its system requirements will be. It may not run in 10.3. I
don't know.
I'm not sure about Illustrator. It may depend on the version you have
installed. If you are not wedded to using PMingLiU, then you have
other options. Adobe supplies a "Ming" font with the Creative Suite CS
and above, and of course there's also the Song-style fonts that come
with OS X. General Chinese font info is here:
http://www.yale.edu/chinesemac/pages/fonts.html
ER