Er, I've never seen someone use kanji as particles
) -- at least not in modern Japanese.
Japanese sentences have only about one organizational rubric: the verb must come last (not counting certain particles, like "ka", which turn the sentence into a question).
The meaning of other things in the sentence are either obvious or they are given by appending an appropriate particle, written in hiragana. Particles indicate things like: subject, object, where-from, where-to, etc.
Kanji come from the Chinese way of writing, applied to the Japanese language. They have intrinsic meaning -- unlike syllabic or alphabetic symbols, which only have a sound attached -- the kanji for "dog" is a specific symbol, distinct from the symbol for "man". Each symbol has a way to "read" (speak) it. (Most have multiple ways to read it, depending on how it is used.)
Symbols may be combined to form more complex words. They may also just be used for their sounds, though this is the exception and not the rule.
Hiragana are just a phonetic way to write Japanese, often used to help children read kanji, in addition to use for words for which the kanji does not exist or is obscure/unknown to the reader (like children), and the aforementioned particles.
Katakana are the same thing except they are used primarily for foreign or foreign-sounding words and names, and for writing sound effects.
Roumaji is used for effect, and for us foreigners.
I just found this too: http://en.wikipedia.org/wiki/Japanese_writing_system
It is a better read than what I wrote here.