Don’t push space as you type? Basically, when you use an IME, pushing space while you’re still editing a word will start listing through the available kanji – you can tell you’re still editing the word, because it’ll be underlined. Hit enter to confirm the word, and the underline will go away, then you can push space all you like.
If you’ve accidentally forgotten and pushed space anyway, you can make it hiragana (again, while still editing the word) by pushing F6. F7 if you want to make it katakana (which is helpful to know if you’re trying to write long katakana words but the IME keeps trying to insert kanji). If you’ve already confirmed the word, you’ll need to delete it and type it again, sadly.
F5 brings up search-by-radical. Never knew I could do that. Maybe I should try playing with the other function keys and see what happens. =)