One thing that link doesn't mention is that before you can do any of this you need to move the font to Windows' fonts folder. Exit PlecoDict completely, using the Quit command in the Dict menu, then use File Explorer to go to \\Program Files\PlecoDict; tap-hold on SimSun and choose "Cut" from the menu that pops up. After that, go to \\Windows\Fonts, tap-hold in an empty space in that window and choose "Paste" to move the font there. Soft reset your Pocket PC (stick a paperclip in the reset hole in the back) and when you open Word again ZYSong should now show up in the list of available fonts.
If you follow ldolse's instructions, that will set it up so that even when displaying English text, your Pocket PC will fall back on ZYSong to display Chinese characters that aren't included in the active font (Tahoma or whatever), so that would make it easier to use Chinese elsewhere on your Pocket PC. However, if you want to actually input Chinese text outside of Pleco you'll need another piece of software for that, CE-Star or Monster Chinese or another Pocket PC Chinese system like those.
