Keyatta-san, they teach you katakana too at Rocket Japanese, just follow the lessons. As for kanji, you are introduced a bit to it, but not a lot. So you could use different sources for Kanji, like mnemonics or flash cards.
Saeed-san, let me explain again how it works:
The particle "ha", when it's used as part of a word like: HAnasu (=to speak), HAtaraku (=to work), HAntai (= opposite), goHAn (=rice) etc., is read as "ha" (exactly how you write it in romanji). - Please note that when it's a part of a word, it can be anywhere within it, not only at the beginning, that's why I mentioned "gohan" as an example too !
On the other hand, when it is used as a particle to mark the topic of a sentence (topic of sentence = the thing to which the sentence is referring to), it's reading changes to "wa". For example:
- わたし は コッド - watashi wa Coddo. Note that the "ha" particle is read "wa", just like the wa in watashi (= I / me). Here, it is used as a particle and mars the "I / ME" word as the topic of the sentence => the sentence is about me.
Pascal-san, I didn't mention the konnichiwa word because I thought it's compounds are obvious: kon - a reading from the character for "now" (今), here meaning "this", nichi = day and the "ha" particle (read as "wa" here) to make an emphasis that I'm talking about this day =>good day :D.
Hope I managed to clarify things a bit,