Code page xxx isn't available on my (windows XP or 2003) computer, what happened?

Use Unicode :) 

Beginning with windows Vista all code pages are installed by default, however in previous versions of windows code page support has to be enabled through intl.cpl (Regional and Language Options in the control panel).  You'll find a tab there for adding code pages.  For some languages the "east asian language support" checkbox also needs installed to enable complete font support.